002 《folly::Preprocessor 权威指南》

                                
                                    

                            
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#include <iostream> // 包含标准库头文件
                        

                            
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#include "my_header.h" // 包含用户自定义头文件
                        
                                
                            

                                
                                    

                            
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#define PI 3.14159 // 定义常量宏
                        

                            
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#define MAX(a, b) ((a) > (b) ? (a) : (b)) // 定义函数式宏
                        
                                
                            

                                
                                    

                            
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#define DEBUG_MODE
                        

                            
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// ... 一些代码 ...
                        

                            
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#undef DEBUG_MODE // 取消 DEBUG_MODE 宏的定义
                        
                                
                            

                                
                                    

                            
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#ifdef _WIN32
                        

                            
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    // Windows 平台特定代码
                        

                            
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    #define SYSTEM_NAME "Windows"
                        

                            
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#elif __linux__
                        

                            
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    // Linux 平台特定代码
                        

                            
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    #define SYSTEM_NAME "Linux"
                        

                            
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#else
                        

                            
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    // 其他平台默认代码
                        

                            
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    #define SYSTEM_NAME "Unknown"
                        

                            
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#endif
                        

                            
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#ifdef DEBUG_MODE
                        

                            
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    std::cout << "Debug mode is enabled." << std::endl;
                        

                            
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#endif
                        

                            
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#if __cplusplus >= 201103L
                        

                            
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    // C++11 或更高版本特性
                        

                            
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    #include <thread>
                        

                            
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#else
                        

                            
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    // 兼容旧版本 C++ 的代码
                        

                            
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    #include <pthread.h>
                        

                            
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#endif
                        
                                
                            

                                
                                    

                            
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#line 100 "my_generated_file.cpp" // 设置当前行号为 100，文件名为 "my_generated_file.cpp"
                        

                            
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// ... 代码 ...
                        
                                
                            

                                
                                    

                            
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#ifndef __cplusplus
                        

                            
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    #error "This code requires a C++ compiler."
                        

                            
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#endif
                        

                            
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#if __cplusplus < 201103L
                        

                            
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    #error "C++11 or higher standard is required."
                        

                            
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#endif
                        
                                
                            

                                
                                    

                            
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#pragma once // 防止头文件被重复包含 (常用 pragma)
                        

                            
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#pragma warning(disable: 4996) // 禁用特定的警告 (MSVC 编译器 pragma)
                        

                            
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#pragma GCC optimize("O3") // 设置优化级别 (GCC 编译器 pragma)
                        
                                
                            

                                
                                    

                            
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#define BUFFER_SIZE 1024
                        

                            
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#define AUTHOR_NAME "John Doe"
                        

                            
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#define VERSION "1.2.3"
                        
                                
                            

                                
                                    

                            
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char buffer[BUFFER_SIZE]; // 预处理后变为 char buffer[1024];
                        

                            
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std::cout << "Author: " << AUTHOR_NAME << ", Version: " << VERSION << std::endl;
                        

                            
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// 预处理后变为 std::cout << "Author: " << "John Doe" << ", Version: " << "1.2.3" << std::endl;
                        
                                
                            

                                
                                    

                            
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#define SQUARE(x) ((x) * (x))
                        

                            
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#define ADD(a, b) ((a) + (b))
                        

                            
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#define PRINT_DEBUG(msg) std::cerr << "DEBUG: " << msg << std::endl
                        
                                
                            

                                
                                    

                            
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#define MAX_USERS 1000
                        

                            
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int users[MAX_USERS];
                        
                                
                            

                                
                                    

                            
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#define PRINT_INT(x) std::cout << #x << " = " << (x) << std::endl
                        

                            
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int value = 42;
                        

                            
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PRINT_INT(value); // 展开后为 std::cout << "value" << " = " << (value) << std::endl;
                        
                                
                            

                                
                                    

                            
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#ifdef DEBUG_MODE
                        

                            
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    #define LOG(msg) std::cerr << "DEBUG: " << msg << std::endl
                        

                            
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#else
                        

                            
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    #define LOG(msg) /* 忽略日志 */
                        

                            
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#endif
                        

                            
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LOG("Function started.");
                        

                            
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// ... 一些代码 ...
                        

                            
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LOG("Function finished.");
                        
                                
                            

                                
                                    

                            
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#ifdef _WIN32
                        

                            
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    // Windows 平台特定代码
                        

                            
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    #include <windows.h>
                        

                            
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    void platform_specific_function() { /* Windows 实现 */ }
                        

                            
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#elif __linux__
                        

                            
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    // Linux 平台特定代码
                        

                            
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    #include <unistd.h>
                        

                            
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    void platform_specific_function() { /* Linux 实现 */ }
                        

                            
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#else
                        

                            
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    // 其他平台默认实现
                        

                            
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    void platform_specific_function() { /* 默认实现 */ }
                        

                            
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#endif
                        
                                
                            

                                
                                    

                            
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#ifdef DEBUG_MODE
                        

                            
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    // 调试版本代码
                        

                            
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    #define LOG(msg) std::cerr << "DEBUG: " << msg << std::endl
                        

                            
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    #define ASSERT(condition) if (!(condition)) { std::cerr << "Assertion failed: " << #condition << std::endl; std::abort(); }
                        

                            
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#else
                        

                            
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    // 发布版本代码
                        

                            
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    #define LOG(msg) /* 忽略日志 */
                        

                            
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    #define ASSERT(condition) /* 忽略断言 */
                        

                            
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#endif
                        

                            
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void process_data(int data) {
                        

                            
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    LOG("Entering process_data with data = " << data);
                        

                            
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    ASSERT(data >= 0); // 断言数据必须非负
                        

                            
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    // ... 数据处理逻辑 ...
                        

                            
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    LOG("Exiting process_data");
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#ifdef FEATURE_A_ENABLED
                        

                            
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    // 启用特性 A 的代码
                        

                            
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    void feature_a() { /* 特性 A 的实现 */ }
                        

                            
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#else
                        

                            
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    // 禁用特性 A 的代码
                        

                            
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    void feature_a() { /* 空实现或提示信息 */ }
                        

                            
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#endif
                        

                            
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#ifdef ENABLE_LOGGING
                        

                            
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    #define LOG_TO_FILE
                        

                            
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#endif
                        

                            
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#ifdef LOG_TO_FILE
                        

                            
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    // 将日志输出到文件
                        

                            
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    void log_message(const std::string& msg) { /* 文件日志实现 */ }
                        

                            
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#else
                        

                            
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    // 将日志输出到控制台
                        

                            
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    void log_message(const std::string& msg) { /* 控制台日志实现 */ }
                        

                            
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#endif
                        
                                
                            

                                
                                    

                            
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#if __cplusplus >= 201103L
                        

                            
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    // C++11 或更高版本特性
                        

                            
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    #include <thread>
                        

                            
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    using namespace std::chrono;
                        

                            
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    void sleep_ms(int ms) { std::this_thread::sleep_for(milliseconds(ms)); }
                        

                            
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#else
                        

                            
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    // 兼容 C++98 的代码
                        

                            
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    #include <unistd.h>
                        

                            
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    void sleep_ms(int ms) { usleep(ms * 1000); }
                        

                            
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#endif
                        
                                
                            

                                
                                    

                            
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#ifndef MY_HEADER_H
                        

                            
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#define MY_HEADER_H
                        

                            
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// 头文件内容
                        

                            
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#endif // MY_HEADER_H
                        
                                
                            

                                
                                    

                            
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#define STRINGIZE(x) #x
                        

                            
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int main() {
                        

                            
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    std::cout << STRINGIZE(Hello, World!) << std::endl; // 输出 "Hello, World!"
                        

                            
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    std::cout << STRINGIZE(123 + 456) << std::endl;    // 输出 "123 + 456"
                        

                            
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    std::cout << STRINGIZE("abc") << std::endl;        // 输出 ""abc"" (注意，会再加一层引号)
                        

                            
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    return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#define PRINT_VAR(var) std::cout << #var << " = " << (var) << std::endl
                        

                            
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int count = 10;
                        

                            
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float price = 99.9;
                        

                            
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PRINT_VAR(count); // 输出 "count = 10"
                        

                            
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PRINT_VAR(price); // 输出 "price = 99.9"
                        
                                
                            

                                
                                    

                            
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#define VERSION_STRING(major, minor, patch) #major "." #minor "." #patch
                        

                            
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std::cout << "Version: " << VERSION_STRING(1, 2, 3) << std::endl; // 输出 "Version: 1.2.3"
                        
                                
                            

                                
                                    

                            
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#define VALUE 100
                        

                            
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#define STRINGIZE_VALUE(x) #x
                        

                            
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#define STRINGIZE_DIRECTLY(x) STRINGIZE(x)
                        

                            
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std::cout << STRINGIZE_VALUE(VALUE) << std::endl;      // 输出 "VALUE" (未展开 VALUE 宏)
                        

                            
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std::cout << STRINGIZE_DIRECTLY(VALUE) << std::endl;   // 输出 "100" (先展开 VALUE 宏，再字符串化)
                        
                                
                            

                                
                                    

                            
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#define JOIN(x, y) x ## y
                        

                            
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int main() {
                        

                            
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    int value123 = 456;
                        

                            
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    std::cout << JOIN(value, 123) << std::endl; // 输出 456 (相当于 std::cout << value123 << std::endl;)
                        

                            
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    #define VAR_NAME(prefix, index) JOIN(prefix, index)
                        

                            
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    int VAR_NAME(data, 0) = 10;
                        

                            
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    int VAR_NAME(data, 1) = 20;
                        

                            
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    std::cout << VAR_NAME(data, 0) << ", " << VAR_NAME(data, 1) << std::endl; // 输出 "10, 20"
                        

                            
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    return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#define CREATE_VARIABLE(name, index) int variable ## index = 0;
                        

                            
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CREATE_VARIABLE(data, 1); // 生成 int variable1 = 0;
                        

                            
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CREATE_VARIABLE(data, 2); // 生成 int variable2 = 0;
                        

                            
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variable1 = 100;
                        

                            
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variable2 = 200;
                        

                            
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std::cout << variable1 << ", " << variable2 << std::endl; // 输出 "100, 200"
                        
                                
                            

                                
                                    

                            
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#define DECLARE_GETTER(type, name)     type get_ ## name() const { return name##_; }
                        

                            
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class MyClass {
                        

                            
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public:
                        

                            
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    DECLARE_GETTER(int, value)
                        

                            
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    DECLARE_GETTER(std::string, message)
                        

                            
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private:
                        

                            
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    int value_ = 42;
                        

                            
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    std::string message_ = "Hello";
                        

                            
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};
                        

                            
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int main() {
                        

                            
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    MyClass obj;
                        

                            
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    std::cout << obj.get_value() << std::endl;   // 输出 42
                        

                            
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    std::cout << obj.get_message() << std::endl; // 输出 "Hello"
                        

                            
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    return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#ifndef FEATURE_FLAG
                        

                            
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#  error "FEATURE_FLAG must be defined for this build!"
                        

                            
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#endif
                        

                            
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int main() {
                        

                            
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  // ... 程序逻辑 ...
                        

                            
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  return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#define ENSURE_MACRO_DEFINED(MACRO_NAME)   FOLLY_PP_EVAL(FOLLY_PP_IF(FOLLY_PP_NOT(FOLLY_PP_DEFINED(MACRO_NAME)),                              FOLLY_PP_ERROR("Macro " #MACRO_NAME " must be defined!")))
                        

                            
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ENSURE_MACRO_DEFINED(BUILD_VERSION)
                        

                            
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int main() {
                        

                            
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  // ... 程序逻辑 ...
                        

                            
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  return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#define IS_INT(T) FOLLY_PP_EVAL(FOLLY_PP_IF(FOLLY_PP_STRINGIZE(T) == "int", 1, 0))
                        

                            
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#define IS_FLOAT(T) FOLLY_PP_EVAL(FOLLY_PP_IF(FOLLY_PP_STRINGIZE(T) == "float", 1, 0))
                        

                            
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#define DISPATCH_FUNCTION(T)   FOLLY_PP_EVAL(FOLLY_PP_IF(IS_INT(T), handle_int, FOLLY_PP_IF(IS_FLOAT(T), handle_float, handle_other)))
                        

                            
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void handle_int() {
                        

                            
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  // 处理 int 类型的逻辑
                        

                            
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  printf("Handling int\n");
                        

                            
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}
                        

                            
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void handle_float() {
                        

                            
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  // 处理 float 类型的逻辑
                        

                            
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  printf("Handling float\n");
                        

                            
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}
                        

                            
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void handle_other() {
                        

                            
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  // 处理其他类型的逻辑
                        

                            
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  printf("Handling other\n");
                        

                            
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}
                        

                            
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int main() {
                        

                            
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  DISPATCH_FUNCTION(int)();    // 调用 handle_int
                        

                            
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  DISPATCH_FUNCTION(float)();  // 调用 handle_float
                        

                            
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  DISPATCH_FUNCTION(double)(); // 调用 handle_other
                        

                            
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  return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#define POWER_OF_TWO(N)   FOLLY_PP_EVAL(FOLLY_PP_FOR(i, 0, N, FOLLY_PP_MUL, 2, 1))
                        

                            
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#define N 5
                        

                            
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#define RESULT POWER_OF_TWO(N) // 编译时计算 2^5 = 32
                        

                            
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int main() {
                        

                            
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  printf("2^%d = %d\n", N, RESULT); // 输出：2^5 = 32
                        

                            
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  return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#define DATA_TYPES (int, float, double)
                        

                            
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#define DEFINE_HANDLER(TYPE)   void handle_##TYPE(TYPE value) {     printf("Handling " #TYPE ": %f\n", (double)value);   }
                        

                            
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FOLLY_PP_SEQ_FOR_EACH(DEFINE_HANDLER, DATA_TYPES)
                        

                            
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int main() {
                        

                            
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  handle_int(10);
                        

                            
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  handle_float(3.14f);
                        

                            
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  handle_double(2.71828);
                        

                            
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  return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#define EMPTY_SEQ ()
                        

                            
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#define NON_EMPTY_SEQ (a, b, c)
                        

                            
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#define IS_SEQ_EMPTY(SEQ) FOLLY_PP_EVAL(FOLLY_PP_SEQ_IS_EMPTY(SEQ))
                        

                            
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#if IS_SEQ_EMPTY(EMPTY_SEQ)
                        

                            
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#  define EMPTY_SEQ_MSG "EMPTY_SEQ is empty"
                        

                            
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#else
                        

                            
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#  define EMPTY_SEQ_MSG "EMPTY_SEQ is not empty"
                        

                            
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#endif
                        

                            
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#if IS_SEQ_EMPTY(NON_EMPTY_SEQ)
                        

                            
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#  define NON_EMPTY_SEQ_MSG "NON_EMPTY_SEQ is empty"
                        

                            
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#else
                        

                            
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#  define NON_EMPTY_SEQ_MSG "NON_EMPTY_SEQ is not empty"
                        

                            
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#endif
                        

                            
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int main() {
                        

                            
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  printf("%s\n", EMPTY_SEQ_MSG);     // 输出：EMPTY_SEQ is empty
                        

                            
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  printf("%s\n", NON_EMPTY_SEQ_MSG); // 输出：NON_EMPTY_SEQ is not empty
                        

                            
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  return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#include <stdio.h>
                        

                            
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#include <ctype.h>
                        

                            
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#define STRING_SEQ (hello, world, folly, preprocessor)
                        

                            
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#define TO_UPPER_STRING(X) to_upper_##X
                        

                            
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#define DEFINE_TO_UPPER_FUNCTION(X)   void TO_UPPER_STRING(X)() {     printf("Original: %s, Upper: %s\n", #X, #X /* 简化，实际应转换为大写 */);   }
                        

                            
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FOLLY_PP_SEQ_FOR_EACH(DEFINE_TO_UPPER_FUNCTION, STRING_SEQ)
                        

                            
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int main() {
                        

                            
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  TO_UPPER_STRING(hello)();
                        

                            
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  TO_UPPER_STRING(world)();
                        

                            
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  TO_UPPER_STRING(folly)();
                        

                            
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  TO_UPPER_STRING(preprocessor)();
                        

                            
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  return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#define UNROLL_INIT(data, i) data[i] = 0;
                        

                            
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int main() {
                        

                            
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  int arr[8];
                        

                            
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  FOLLY_PP_REPEAT(4, UNROLL_INIT, arr); // 展开循环 4 次
                        

                            
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  for (int i = 0; i < 8; ++i) {
                        

                            
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    printf("arr[%d] = %d\n", i, arr[i]);
                        

                            
12
                            
  }
                        

                            
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  return 0;
                        

                            
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}
                        
                                
                            

                                
                                    

                            
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arr[0] = 0;
                        

                            
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arr[1] = 0;
                        

                            
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arr[2] = 0;
                        

                            
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arr[3] = 0;
                        
                                
                            

                                
                                    

                            
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#include <folly/Preprocessor.h>
                        

                            
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#define TYPES (int, float, double)
                        

                            
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#define DEFINE_HANDLER_AND_INIT(data, type)   void handle_##type() {     printf("Handling type: %s\n", #type);   }   int init_##type = 0; // 初始化变量
                        

                            
6
                            

                        

                            
7
                            
FOLLY_PP_FOR_EACH(DEFINE_HANDLER_AND_INIT, _, TYPES)
                        

                            
8
                            

                        

                            
9
                            
int main() {
                        

                            
10
                            
  handle_int();
                        

                            
11
                            
  handle_float();
                        

                            
12
                            
  handle_double();
                        

                            
13
                            
  printf("init_int = %d\n", init_int);
                        

                            
14
                            
  printf("init_float = %d\n", init_float);
                        

                            
15
                            
  printf("init_double = %d\n", init_double);
                        

                            
16
                            
  return 0;
                        

                            
17
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
#include <folly/Preprocessor.h>
                        

                            
2
                            
#include <stdio.h>
                        

                            
3
                            

                        

                            
4
                            
#define DEBUG_VAR(var)   printf("Variable: %s, Value: %d\n", FOLLY_PP_STRINGIZE(var), var)
                        

                            
5
                            

                        

                            
6
                            
#define COUNT 10
                        

                            
7
                            

                        

                            
8
                            
int main() {
                        

                            
9
                            
  int my_count = COUNT;
                        

                            
10
                            
  DEBUG_VAR(my_count); // 输出变量名和值
                        

                            
11
                            
  return 0;
                        

                            
12
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
#include <folly/Preprocessor.h>
                        

                            
2
                            
#include <stdio.h>
                        

                            
3
                            

                        

                            
4
                            
#define DEFINE_TYPE_API(prefix, type)   void FOLLY_PP_JOIN(prefix, _create_)(type value) {     printf("Creating %s with value: %f\n", FOLLY_PP_STRINGIZE(FOLLY_PP_JOIN(prefix, _type)), (double)value);   }   type FOLLY_PP_JOIN(prefix, _value_);
                        

                            
5
                            

                        

                            
6
                            
DEFINE_TYPE_API(int, int)
                        

                            
7
                            
DEFINE_TYPE_API(float, float)
                        

                            
8
                            

                        

                            
9
                            
int main() {
                        

                            
10
                            
  int_create_(10);
                        

                            
11
                            
  float_create_(3.14f);
                        

                            
12
                            
  int int_v = int_value_;
                        

                            
13
                            
  float float_v = float_value_;
                        

                            
14
                            
  return 0;
                        

                            
15
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
#include <folly/Preprocessor.h>
                        

                            
2
                            

                        

                            
3
                            
// 定义平台宏，可以在编译时通过 -D 选项指定
                        

                            
4
                            
#if FOLLY_IS_LINUX
                        

                            
5
                            
#define PLATFORM_NAME "Linux"
                        

                            
6
                            
#define FEATURE_A_ENABLED 1
                        

                            
7
                            
#define DEFAULT_PORT 8080
                        

                            
8
                            
#elif FOLLY_IS_MAC
                        

                            
9
                            
#define PLATFORM_NAME "macOS"
                        

                            
10
                            
#define FEATURE_A_ENABLED 0
                        

                            
11
                            
#define DEFAULT_PORT 80
                        

                            
12
                            
#elif FOLLY_IS_WINDOWS
                        

                            
13
                            
#define PLATFORM_NAME "Windows"
                        

                            
14
                            
#define FEATURE_A_ENABLED 1
                        

                            
15
                            
#define DEFAULT_PORT 443
                        

                            
16
                            
#else
                        

                            
17
                            
#define PLATFORM_NAME "Unknown"
                        

                            
18
                            
#define FEATURE_A_ENABLED 0
                        

                            
19
                            
#define DEFAULT_PORT 80
                        

                            
20
                            
#endif
                        

                            
21
                            

                        

                            
22
                            
#ifndef FEATURE_A_ENABLED
                        

                            
23
                            
#define FEATURE_A_ENABLED 0 // 默认禁用 Feature A
                        

                            
24
                            
#endif
                        

                            
25
                            

                        

                            
26
                            
#ifndef DEFAULT_PORT
                        

                            
27
                            
#define DEFAULT_PORT 80 // 默认端口
                        

                            
28
                            
#endif
                        

                            
29
                            

                        

                            
30
                            
void print_config() {
                        

                            
31
                            
  std::cout << "Platform: " << PLATFORM_NAME << std::endl;
                        

                            
32
                            
  std::cout << "Feature A Enabled: " << FEATURE_A_ENABLED << std::endl;
                        

                            
33
                            
  std::cout << "Default Port: " << DEFAULT_PORT << std::endl;
                        

                            
34
                            

                        

                            
35
                            
#if FEATURE_A_ENABLED
                        

                            
36
                            
  std::cout << "Feature A is enabled for this platform." << std::endl;
                        

                            
37
                            
#else
                        

                            
38
                            
  std::cout << "Feature A is disabled for this platform." << std::endl;
                        

                            
39
                            
#endif
                        

                            
40
                            
}
                        

                            
41
                            

                        

                            
42
                            
int main() {
                        

                            
43
                            
  print_config();
                        

                            
44
                            
  return 0;
                        

                            
45
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
g++ -DFOLLY_IS_LINUX config_example.cpp -o config_example
                        

                            
2
                            
./config_example
                        
                                
                            

                                
                                    

                            
1
                            
输出：
                        
                                
                            

                                
                                    

                            
1
                            
Platform: Linux
                        

                            
2
                            
Feature A Enabled: 1
                        

                            
3
                            
Default Port: 8080
                        

                            
4
                            
Feature A is enabled for this platform.
                        
                                
                            

                                
                                    

                            
1
                            
g++ -DFOLLY_IS_MAC config_example.cpp -o config_example
                        

                            
2
                            
./config_example
                        
                                
                            

                                
                                    

                            
1
                            
输出：
                        
                                
                            

                                
                                    

                            
1
                            
Platform: macOS
                        

                            
2
                            
Feature A Enabled: 0
                        

                            
3
                            
Default Port: 80
                        

                            
4
                            
Feature A is disabled for this platform.
                        
                                
                            

                                
                                    

                            
1
                            
g++ -DFOLLY_IS_WINDOWS config_example.cpp -o config_example
                        

                            
2
                            
./config_example
                        
                                
                            

                                
                                    

                            
1
                            
输出：
                        
                                
                            

                                
                                    

                            
1
                            
Platform: Windows
                        

                            
2
                            
Feature A Enabled: 1
                        

                            
3
                            
Default Port: 443
                        

                            
4
                            
Feature A is enabled for this platform.
                        
                                
                            

                                
                                    

                            
1
                            
#include <folly/Preprocessor.h>
                        

                            
2
                            
#include <iostream>
                        

                            
3
                            
#include <string>
                        

                            
4
                            
#include <type_traits>
                        

                            
5
                            

                        

                            
6
                            
// 定义一个特征宏 IS_STRING，用于判断类型是否为 std::string
                        

                            
7
                            
#define IS_STRING(T) std::is_same<std::decay_t<T>, std::string>::value
                        

                            
8
                            

                        

                            
9
                            
// 定义通用打印函数宏 PRINT_VALUE
                        

                            
10
                            
#define PRINT_VALUE(value)                                            std::cout << "Value: ";                                            FOLLY_IF(IS_STRING(value)) {                                         std::cout << value << " (string)" << std::endl;                  } FOLLY_ELSE {                                                       std::cout << value << " (other type)" << std::endl;             } FOLLY_ENDIF
                        

                            
11
                            

                        

                            
12
                            
// 自定义类型
                        

                            
13
                            
struct MyType {
                        

                            
14
                            
  int value;
                        

                            
15
                            
};
                        

                            
16
                            

                        

                            
17
                            
std::ostream& operator<<(std::ostream& os, const MyType& obj) {
                        

                            
18
                            
  os << "MyType(" << obj.value << ")";
                        

                            
19
                            
  return os;
                        

                            
20
                            
}
                        

                            
21
                            

                        

                            
22
                            

                        

                            
23
                            
int main() {
                        

                            
24
                            
  int int_val = 10;
                        

                            
25
                            
  float float_val = 3.14f;
                        

                            
26
                            
  std::string str_val = "hello";
                        

                            
27
                            
  MyType my_val = {42};
                        

                            
28
                            

                        

                            
29
                            
  PRINT_VALUE(int_val);
                        

                            
30
                            
  PRINT_VALUE(float_val);
                        

                            
31
                            
  PRINT_VALUE(str_val);
                        

                            
32
                            
  PRINT_VALUE(my_val);
                        

                            
33
                            

                        

                            
34
                            
  return 0;
                        

                            
35
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
g++ traits_example.cpp -o traits_example -std=c++11
                        

                            
2
                            
./traits_example
                        
                                
                            

                                
                                    

                            
1
                            
Value: 10 (other type)
                        

                            
2
                            
Value: 3.14 (other type)
                        

                            
3
                            
Value: hello (string)
                        

                            
4
                            
Value: MyType(42) (other type)
                        
                                
                            

                                
                                    

                            
1
                            
#include <folly/Preprocessor.h>
                        

                            
2
                            
#include <iostream>
                        

                            
3
                            
#include <algorithm>
                        

                            
4
                            
#include <vector>
                        

                            
5
                            

                        

                            
6
                            
// 定义数组大小阈值宏
                        

                            
7
                            
#ifndef SORT_THRESHOLD
                        

                            
8
                            
#define SORT_THRESHOLD 10 // 默认阈值为 10
                        

                            
9
                            
#endif
                        

                            
10
                            

                        

                            
11
                            
// 插入排序算法 (仅为示例，实际应用中可以使用更高效的实现)
                        

                            
12
                            
template <typename T>
                        

                            
13
                            
void insertion_sort(std::vector<T>& arr) {
                        

                            
14
                            
  int n = arr.size();
                        

                            
15
                            
  for (int i = 1; i < n; ++i) {
                        

                            
16
                            
    T key = arr[i];
                        

                            
17
                            
    int j = i - 1;
                        

                            
18
                            
    while (j >= 0 && arr[j] > key) {
                        

                            
19
                            
      arr[j + 1] = arr[j];
                        

                            
20
                            
      j = j - 1;
                        

                            
21
                            
    }
                        

                            
22
                            
    arr[j + 1] = key;
                        

                            
23
                            
  }
                        

                            
24
                            
}
                        

                            
25
                            

                        

                            
26
                            
// 快速排序算法 (仅为示例，实际应用中可以使用更高效的实现)
                        

                            
27
                            
template <typename T>
                        

                            
28
                            
void quick_sort(std::vector<T>& arr) {
                        

                            
29
                            
  std::sort(arr.begin(), arr.end()); // 使用 std::sort 简化快速排序的实现
                        

                            
30
                            
}
                        

                            
31
                            

                        

                            
32
                            
// 通用排序函数宏 SORT_ARRAY
                        

                            
33
                            
#define SORT_ARRAY(arr)                                                 std::cout << "Sorting array using ";                                  FOLLY_IF(arr.size() <= SORT_THRESHOLD) {                               std::cout << "insertion sort." << std::endl;                         insertion_sort(arr);                                              } FOLLY_ELSE {                                                         std::cout << "quick sort." << std::endl;                            quick_sort(arr);                                                  } FOLLY_ENDIF
                        

                            
34
                            

                        

                            
35
                            

                        

                            
36
                            
int main() {
                        

                            
37
                            
  std::vector<int> small_array = {5, 2, 8, 1, 9, 4};
                        

                            
38
                            
  std::vector<int> large_array = {15, 2, 8, 1, 9, 4, 12, 7, 18, 3, 11, 6, 19, 5, 14, 10, 17, 13, 16};
                        

                            
39
                            

                        

                            
40
                            
  std::cout << "Before sorting small array: ";
                        

                            
41
                            
  for (int val : small_array) std::cout << val << " ";
                        

                            
42
                            
  std::cout << std::endl;
                        

                            
43
                            
  SORT_ARRAY(small_array);
                        

                            
44
                            
  std::cout << "After sorting small array: ";
                        

                            
45
                            
  for (int val : small_array) std::cout << val << " ";
                        

                            
46
                            
  std::cout << std::endl;
                        

                            
47
                            

                        

                            
48
                            
  std::cout << "Before sorting large array: ";
                        

                            
49
                            
  for (int val : large_array) std::cout << val << " ";
                        

                            
50
                            
  std::cout << std::endl;
                        

                            
51
                            
  SORT_ARRAY(large_array);
                        

                            
52
                            
  std::cout << "After sorting large array: ";
                        

                            
53
                            
  for (int val : large_array) std::cout << val << " ";
                        

                            
54
                            
  std::cout << std::endl;
                        

                            
55
                            

                        

                            
56
                            
  return 0;
                        

                            
57
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
g++ static_polymorphism_example.cpp -o static_polymorphism_example -std=c++11
                        

                            
2
                            
./static_polymorphism_example
                        
                                
                            

                                
                                    

                            
1
                            
Before sorting small array: 5 2 8 1 9 4
                        

                            
2
                            
Sorting array using insertion sort.
                        

                            
3
                            
After sorting small array: 1 2 4 5 8 9
                        

                            
4
                            
Before sorting large array: 15 2 8 1 9 4 12 7 18 3 11 6 19 5 14 10 17 13 16
                        

                            
5
                            
Sorting array using quick sort.
                        

                            
6
                            
After sorting large array: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
                        
                                
                            

                                
                                    

                            
1
                            
#include <folly/Preprocessor.h>
                        

                            
2
                            
#include <iostream>
                        

                            
3
                            
#include <string>
                        

                            
4
                            

                        

                            
5
                            
class MyClass {
                        

                            
6
                            
 private:
                        

                            
7
                            
  int value1_;
                        

                            
8
                            
  std::string value2_;
                        

                            
9
                            
  float value3_;
                        

                            
10
                            

                        

                            
11
                            
 public:
                        

                            
12
                            
  MyClass(int v1, std::string v2, float v3) : value1_(v1), value2_(v2), value3_(v3) {}
                        

                            
13
                            

                        

                            
14
                            
  // 使用 FOR_EACH_TUPLE 宏生成 getter 函数
                        

                            
15
                            
  #define GENERATE_GETTER(tuple)                                              ReturnType(GET_TYPE(tuple))                                              FunctionName(GET_NAME(tuple))() const {                                     std::cout << "Accessing member: " << STRINGIZE(GET_NAME(tuple)) << std::endl;       return member_variable_;                                                }
                        

                            
16
                            

                        

                            
17
                            
  #define GET_TYPE(tuple) FOLLY_PP_TUPLE_ELEM(0, tuple)
                        

                            
18
                            
  #define GET_NAME(tuple) FOLLY_PP_TUPLE_ELEM(1, tuple)
                        

                            
19
                            
  #define ReturnType(type) type
                        

                            
20
                            
  #define FunctionName(name) get_##name
                        

                            
21
                            
  #define member_variable_ FOLLY_PP_CAT(value, STRINGIZE(GET_NAME(tuple)))_
                        

                            
22
                            

                        

                            
23
                            
  FOLLY_PP_FOR_EACH_TUPLE(GENERATE_GETTER,
                        

                            
24
                            
                           ((int, value1), (std::string, value2), (float, value3)))
                        

                            
25
                            

                        

                            
26
                            
  #undef GENERATE_GETTER
                        

                            
27
                            
  #undef GET_TYPE
                        

                            
28
                            
  #undef GET_NAME
                        

                            
29
                            
  #undef ReturnType
                        

                            
30
                            
  #undef FunctionName
                        

                            
31
                            
  #undef member_variable_
                        

                            
32
                            

                        

                            
33
                            
  void print_all_values() const {
                        

                            
34
                            
    std::cout << "Value 1: " << get_value1() << std::endl;
                        

                            
35
                            
    std::cout << "Value 2: " << get_value2() << std::endl;
                        

                            
36
                            
    std::cout << "Value 3: " << get_value3() << std::endl;
                        

                            
37
                            
  }
                        

                            
38
                            
};
                        

                            
39
                            

                        

                            
40
                            

                        

                            
41
                            
int main() {
                        

                            
42
                            
  MyClass obj(100, "example", 2.718f);
                        

                            
43
                            
  obj.print_all_values();
                        

                            
44
                            
  return 0;
                        

                            
45
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
int get_value1() const {
                        

                            
2
                            
  std::cout << "Accessing member: value1" << std::endl;
                        

                            
3
                            
  return value1_;
                        

                            
4
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
g++ simplify_boilerplate_example.cpp -o simplify_boilerplate_example -std=c++11
                        

                            
2
                            
./simplify_boilerplate_example
                        
                                
                            

                                
                                    

                            
1
                            
Accessing member: value1
                        

                            
2
                            
Value 1: 100
                        

                            
3
                            
Accessing member: value2
                        

                            
4
                            
Value 2: example
                        

                            
5
                            
Accessing member: value3
                        

                            
6
                            
Value 3: 2.718
                        
                                
                            

                                
                                    

                            
1
                            
#define PI 3.1415926
                        
                                
                            

                                
                                    

                            
1
                            
#define MAX(a, b) ((a) > (b) ? (a) : (b))
                        
                                
                            

                                
                                    

                            
1
                            
#define STRINGIZE(x) #x
                        
                                
                            

                                
                                    

                            
1
                            
#define JOIN(x, y) x##y
                        
                                
                            

                                
                                    

                            
1
                            
g++ -E your_code.cpp -o preprocessed_code.cpp
                        

                            
2
                            
clang++ -E your_code.cpp -o preprocessed_code.cpp
                        
                                
                            

                                
                                    

                            
1
                            
#define ASSERT(condition)   do {     if (!(condition)) {       fprintf(stderr, "Assertion failed: %s, file: %s, line: %d\n", #condition, __FILE__, __LINE__);       abort();     }   } while (0)
                        
                                
                            

                                
                                    

                            
1
                            
#define SQUARE(x) ((x) * (x))
                        

                            
2
                            
int i = 5;
                        

                            
3
                            
int result = SQUARE(++i); // 展开为 ((++i) * (++i))
                        
                                
                            

                                
                                    

                            
1
                            
#define MUL(a, b) a * b
                        

                            
2
                            
int result = MUL(2 + 3, 4); // 展开为 2 + 3 * 4，结果为 14，而不是预期的 20
                        
                                
                            

                                
                                    

                            
1
                            
#define MUL(a, b) ((a) * (b))
                        
                                
                            

                                
                                    

                            
1
                            
#include <folly/Preprocessor.h>
                        

                            
2
                            

                        

                            
3
                            
#define DEBUG_LEVEL 2
                        

                            
4
                            

                        

                            
5
                            
// 条件编译宏示例
                        

                            
6
                            
#if FOLLY_PP_BOOL(DEBUG_LEVEL > 1)
                        

                            
7
                            
  #define LOG_LEVEL_HIGH
                        

                            
8
                            
#else
                        

                            
9
                            
  #define LOG_LEVEL_LOW
                        

                            
10
                            
#endif
                        

                            
11
                            

                        

                            
12
                            
// 循环宏示例
                        

                            
13
                            
#define PRINT_INDEX(index) std::cout << "Index: " << index << std::endl;
                        

                            
14
                            
#define REPEAT_PRINT(count) FOLLY_PP_REPEAT(count, PRINT_INDEX)
                        

                            
15
                            

                        

                            
16
                            
// 静态断言宏示例
                        

                            
17
                            
#define ARRAY_SIZE 10
                        

                            
18
                            
FOLLY_PP_ASSERT(ARRAY_SIZE > 0);
                        

                            
19
                            

                        

                            
20
                            
int main() {
                        

                            
21
                            
  #ifdef LOG_LEVEL_HIGH
                        

                            
22
                            
    std::cout << "Log level: High" << std::endl;
                        

                            
23
                            
  #else
                        

                            
24
                            
    std::cout << "Log level: Low" << std::endl;
                        

                            
25
                            
  #endif
                        

                            
26
                            

                        

                            
27
                            
  std::cout << "Repeating print:" << std::endl;
                        

                            
28
                            
  REPEAT_PRINT(3);
                        

                            
29
                            

                        

                            
30
                            
  return 0;
                        

                            
31
                            
}
                        
                                
                            

                                
                                    

                            
1
                            
#include <folly/Preprocessor.h>
                        

                            
2
                            
#include <iostream>
                        

                            
3
                            

                        

                            
4
                            
#define VAR_NAME(suffix) FOLLY_PP_JOIN(variable_, suffix)
                        

                            
5
                            
#define STRING_VALUE(x) FOLLY_PP_STRINGIZE(x)
                        

                            
6
                            

                        

                            
7
                            
#define EMPTY_SEQUENCE
                        

                            
8
                            
#define NON_EMPTY_SEQUENCE(a, b, c) a, b, c
                        

                            
9
                            

                        

                            
10
                            
int main() {
                        

                            
11
                            
  int VAR_NAME(count) = 10; // 展开为 variable_count
                        

                            
12
                            
  std::cout << "Variable value: " << variable_count << std::endl;
                        

                            
13
                            

                        

                            
14
                            
  std::cout << "Stringized value: " << STRING_VALUE(Hello_World) << std::endl; // 展开为 "Hello_World"
                        

                            
15
                            

                        

                            
16
                            
  std::cout << "Is EMPTY_SEQUENCE empty? " << FOLLY_PP_IS_EMPTY(EMPTY_SEQUENCE) << std::endl; // 输出 1 (true)
                        

                            
17
                            
  std::cout << "Is NON_EMPTY_SEQUENCE empty? " << FOLLY_PP_IS_EMPTY(NON_EMPTY_SEQUENCE(1,2,3)) << std::endl; // 输出 0 (false)
                        

                            
18
                            
  std::cout << "Size of NON_EMPTY_SEQUENCE: " << FOLLY_PP_VARIADIC_SIZE(NON_EMPTY_SEQUENCE(1,2,3)) << std::endl; // 输出 3
                        

                            
19
                            

                        

                            
20
                            
  return 0;
                        

                            
21
                            
}