#include "QtWidgetsApplication1.h"
#include <QtWidgets/QApplication>

#include <QtDebug>
#include <QFile>
#include <QTextStream>
#include <QDateTime>
#include <QMutex>
#include <QString>


void outputMessage(QtMsgType type, const QMessageLogContext& context, const
 
 QString& msg)
{
    static QMutex mutex;
    mutex.lock();

    QString text;
    switch (type) {
    case QtDebugMsg:
        text = QString("debug:");
        break;
    case QtWarningMsg:
        text = QString("warning:");
        break;
    }

    QString context_info = QString("File:(%1) Line:(%2)
 
").arg(QString(context.file)).arg(context.line);
    QString current_date_time = QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss ddd");
    QString current_date = QString("(%1)").arg(current_date_time);
    QString message = QString("%1 %2 %3 %4").arg(text).arg(context_info).arg(msg).arg(current_date);

    QFile file(
 
"log.txt");
    file.open(QIODevice::WriteOnly | QIODevice::Append);
    QTextStream text_stream(&file);
    text_stream << message << "\r\n";
    file.flush();
    file.close();

    mutex.unlock();
}


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    qInstallMessageHandler(outputMessage);
    QtWidgetsApplication1 w;
    w.show();
    qDebug("this is first log text");
    return a.exec();
}

然後生成後 執行就可以看見日誌檔案了