C++ 自定义的线程安全的LOG_PRINTF

1、log.h中宏定义

#ifndef LOG_H
#define LOG_H

#include <stdio.h>
#include <iostream>
#include <chrono>
#include <ctime>
#include <mutex>

#define LOG_PRINTF(format, ...) do{ \
    static std::mutex log_mutex;\
    auto now = std::chrono::system_clock::now();\
    std::time_t  now_time_t = std::chrono::system_clock::to_time_t(now);\
    auto duration = now.time_since_epoch();\
    auto milliseconds = static_cast<int>(std::chrono::duration_cast<std::chrono::milliseconds>(duration).count() % 1000);\
    std::lock_guard<std::mutex> guard(log_mutex);\
    std::tm now_tm; \
    localtime_s(&now_tm, &now_time_t);\
    printf("[%04d-%02d-%02d %02d:%02d:%02d.%03d]" format, \
           now_tm.tm_year + 1900 , now_tm.tm_mon + 1, now_tm.tm_mday, \
           now_tm.tm_hour, now_tm.tm_min , now_tm.tm_sec, milliseconds, ##__VA_ARGS__);\
}while(0)

#endif // LOG_H

2、main.cpp 使用

FILE *logFile = freopen("log.txt","a",stdout);
if(logFile == NULL) {
   perror("Failed to open or creat log file");
}

fclose(logFile); // 关闭文件，退出程序使用

3、Qt 中使用示例

3.1 修改前

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec(); // 运行 Qt 事件循环
}

3.2 修改后

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    
    FILE *logFile = freopen("log.txt","a",stdout);
    if(logFile == NULL) {
       perror("Failed to open or creat log file");
    }
    
    MainWindow w;
    w.show();
    
    int result = a.exec(); // 运行 Qt 事件循环
    fclose(logFile); // 退出 Qt 事件循环后关闭日志文件
    return result;
}

3.3 遗留问题(宏中条件编译的问题)

Windows线程安全:
localtime_s(&now_tm, &now_time_t);
Linux(POSIX)线程安全:
localtime_r(&now_time_t, &now_tm);