Redirect QDebug output to a file.

redirectQDebug.cpp

/*
This code redirects the output of qDebug() to a log file.
It also rotates the file base on size.
Uses QMutex for thread safety.
*/

//some constants to parameterize.
const qint64 LOG_FILE_LIMIT = 3000000;
const QString LOG_PATH = "/application/logs/";
const QString LOG_FILENAME = "mylogfile.log";

    //thread safety
    QMutex mutex;
    
void redirectDebugMessages(QtMsgType type, const QMessageLogContext & context, const QString & str)
{
    //thread safety
    mutex.lock();
    QString txt;
  
    //prepend timestamp to every message
    QString datetime = QDateTime::currentDateTime().toString("yyyy.MM.dd hh:mm:ss");
    //prepend a log level label to every message
    switch (type) {
    case QtDebugMsg:
        txt = QString("[Debug*] ");
        break;
    case QtWarningMsg:
        txt = QString("[Warning] ");
    break;
    case QtInfoMsg:
        txt = QString("[Info] ");
    break;
    case QtCriticalMsg:
        txt = QString("[Critical] ");
    break;
    case QtFatalMsg:
        txt = QString("[Fatal] ");
    }
  
    QString filePath = LOG_PATH + LOG_FILENAME;
    QFile outFile(filePath);
  
    //if file reached the limit, rotate to filename.1
    if(outFile.size() > LOG_FILE_LIMIT){
        //roll the log file.
        QFile::remove(filePath + ".1");
        QFile::rename(filePath, filePath + ".1");
        QFile::resize(filePath, 0);
    }
  
    //write message
    outFile.open(QIODevice::WriteOnly | QIODevice::Append);
    QTextStream ts(&outFile);
    ts << datetime << txt << str << endl;
  
    //close fd
    outFile.close();
    mutex.unlock();
}

//in the main function add this code

int main(int argc, char *argv[]){
 
  qInstallMessageHandler(redirectDebugMessages);
  
}

Nice catch! Thanks