void qDebugMsgHandler(QtMsgType type, const QMessageLogContext& context, const QString& strMsg) {
    QString strOutput;

    if ( context.file ) {
        strOutput += QString(context.file);

        if ( context.function ) {
            if ( context.line > 0 ) {
                strOutput += QString(" L%1").arg(context.line, 8, 10, QChar('0')) + QString(":");
            }
            strOutput += QString(context.function);
        }
    }
    if ( strMsg.length() > 0 ) {
        if ( strOutput.length() > 0 ) {
            strOutput += ": ";
        }
        strOutput += strMsg;
    }
    switch( type ) {
    case QtDebugMsg:
        fprintf(stderr, "   Debug:%s\n", strOutput.toLatin1().data());
        break;
    case QtInfoMsg:
        fprintf(stderr, "    Info:%s\n", strOutput.toLatin1().data());
        break;
    case QtWarningMsg:
        fprintf(stderr, " Warning:%s\n", strOutput.toLatin1().data());
        break;
    case QtCriticalMsg:
        fprintf(stderr, "Critical:%s\n", strOutput.toLatin1().data());
        break;
    case QtFatalMsg:
        fprintf(stderr, "   Fatal:%s\n", strOutput.toLatin1().data());
        break;
    }
    fflush(stderr);
}

This is installed when my application starts:

int main(int argc, char *argv[]) {
    if ( argc < 2 ) {
        error(static_cast<const char*>("Please specify configuration file!"));
   }
    QString strConfig = QString(argv[1]);
    //Install custom message handler
    qInstallMessageHandler(qDebugMsgHandler);

Although every call to this handler ends with a flush(stderr), there are times when I know calls to qDebug has been called but I do not see anything in the Application Output, sometimes for a very long time.

It seems that the call to fflush isn't enough ?