QT, using qDebug() with custom message handler does not show line/file/function info-CodePudding

I have the following code taken from https://doc.qt.io/qt-5/qtglobal.html#qInstallMessageHandler I want to have access to context.file, context.line, context.function inside myMessageOutput()

void myMessageOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
    QByteArray localMsg = msg.toLocal8Bit();
    const char *file = context.file ? context.file : "";
    const char *function = context.function ? context.function : "";
    switch (type) {
    case QtDebugMsg:
        fprintf(stderr, "Debug: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    case QtInfoMsg:
        fprintf(stderr, "Info: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    case QtWarningMsg:
        fprintf(stderr, "Warning: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    case QtCriticalMsg:
        fprintf(stderr, "Critical: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    case QtFatalMsg:
        fprintf(stderr, "Fatal: %s (%s:%u, %s)\n", localMsg.constData(), file, context.line, function);
        break;
    }
}

int main(int argc, char **argv)
{
    qInstallMessageHandler(myMessageOutput);
    QApplication app(argc, argv);
    ...
    return app.exec();
}

In Debug build (using `qDebug() << "test logging") shows details about context.line/file/number. In Release build that info(s) are nullptr or 0 (line). Reproduced on Windows (QT 5.12)

CodePudding user response：

I have tested your code in Qt 5.15.2 with gcc (in Linux) and it worked both in debug and release mode and I can not reproduce your problem. However it is mentioned in document page QMessageLogContext Class that:

Note: By default, this information is recorded only in debug builds. You can overwrite this explicitly by defining QT_MESSAGELOGCONTEXT or QT_NO_MESSAGELOGCONTEXT.

So adding following line to your project.pro file may fix your problem:

DEFINES = QT_MESSAGELOGCONTEXT

Do not forget to run qmake and rebuild your project to see effects.