Qt5:如何使用qDebug()登录文件，多线程应用程序 [英] Qt5: How to use qDebug() to log in a file, multi-thread application

问题描述

几天前我开始使用Qt5.我的应用程序需要一个 logger ，因此我决定使用qDebug，但是为了将日志存储在文件中，似乎必须对其进行重定向".

I started using Qt5 few days ago. I needed a logger for my app and I decided to use qDebug, but it seems it has to be "redirected" in order to have the logs in a file.

我使用qInstallMessageHandler来做到这一点，并编写了如下所示的自己的处理程序(灵感来自此处的其他人).

I used qInstallMessageHandler to do that and I wrote my own handler as presented below (inspired from other people here).

似乎可行，但由于我不是专家，所以我不得不问: 可以在多线程应用程序中使用它吗?

It seems it works, but as I am not a guru, I have to ask: Is it ok to use this in a multi-thread application or not?

此外，如果可以在多线程应用程序中使用安全/安全，是否可以通过某种方式对其进行改进?

Also, if it is ok/safe for using in a multi-thread app, can it be improved somehow?

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

    QDateTime dateTime(QDateTime::currentDateTime());

    QString timeStr(dateTime.toString("dd-MM-yyyy HH:mm:ss:zzz"));
    QString contextString(QString("(%1, %2)").arg(context.file).arg(context.line));

    QFile outFile("file.log");
    outFile.open(QIODevice::WriteOnly | QIODevice::Append);

    QTextStream stream(&outFile);
    stream << timeStr << " " << contextString << ": " << msg << endl;

    mutex.unlock();
}

推荐答案

您的方法看起来简单而干净.我会那样保留.

Your approach looks simple and clean. I'd keep it like that.

您可以改进一件事:在应用程序启动时仅打开一次文件，在关闭应用程序时将其关闭.打开文件是一项昂贵的操作.

There is one thing you can improve: Open the file only once at application start and close it when you close the application. Opening a file is an expensive operation.

您可以从多个线程中写入同一打开文件，因为互斥锁可确保只有一个线程在同一时间写入.

You can write into the same open file from multiple threads, since your mutex ensures that only one thread writes at the same time.

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