将打印信息（qDebug、qInfo、qWarning、qCritial等）输出到指定文件来以实现简单的日志功能。

#include "mainwindow.h"
#include <QApplication>
#include <QLoggingCategory>
#include <QMutex>
#include <QDateTime>
#include <QDir>
#include <QFileInfo>
QString logDirName = "log";
QMutex mutex;
void logInit();
void message(QtMsgType type, const QMessageLogContext &context, const QString &msg);
int main(int argc, char *argv[])
{
    logInit();
    QApplication a(argc, argv);
    qDebug()<<"aaaa";
    MainWindow w;
    w.show();
    return a.exec();
}

void logInit()
{
    QDir dir(logDirName);
    // 不存在log目录就先创建
    if (!dir.exists()) QDir().mkdir(logDirName);
    // 遍历日志目录所有日志文件，然后删除十天前的日志文件
    QFileInfoList logList = dir.entryInfoList({"*.txt"}, QDir::Files, QDir::Time);
    foreach (const QFileInfo &info, logList) {
        if (info.created().daysTo(QDateTime::currentDateTime()) > 10) dir.remove(info.fileName());
    }
    QLoggingCategory::setFilterRules("*.info=true\n");
    qInstallMessageHandler(message);
}

void message(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
    mutex.lock();
    QString text = QString();
    switch (type) {
    case QtDebugMsg:
        text = "Debug";
        break;
    case QtWarningMsg:
        text = "Warning";
        break;
    case QtCriticalMsg:
        text = "Critical";
        break;
    case QtInfoMsg:
        text = "Info";
        break;
    case QtFatalMsg:
        text = "Fatal";
        break;
    default:
        break;
    }
    QString log
        = QString("[%1:%2:%3:%4]%5:%6").arg(QDateTime::currentDateTime().toString(
                                                "yyyy-MM-dd hh:mm:ss.zzz")).arg(context.file).arg(
              context.function).arg(context.line).arg(text).arg(msg);
    static QString path = QDir::cleanPath(
        logDirName+QDir::separator()+QDateTime::currentDateTime().toString(
            "yyyyMMdd-hhmmsszzz")+QString("LOG.txt"));
    QFile file(path);
    if (file.open(QIODevice::WriteOnly|QIODevice::Append)) {
        QTextStream stream(&file);
        stream<<log<<endl;
        file.flush();
        file.close();
    }
    mutex.unlock();
}

该项目内所有打印信息将会输出到指定文件，比如在主界面mainwindow中点击按钮印一句d

void MainWindow::on_pushButton_clicked()
{
    qDebug()<<"11111";
}

程序运行后，不停点击按钮，可以看到有生成对应文件