#include <QCoreApplication>
#include <QDateTime>

FILE *flogfile;

void msg_handler(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
    // https://doc.qt.io/qt-5/qtglobal.html#qInstallMessageHandler

    const char *func = context.function ? context.function : "unknown function";
    const char *file = context.file ? context.file : "";

    QString dt = QDateTime::currentDateTime().toString();
    fprintf(flogfile, "[%s] ", qPrintable(dt));
    switch (type) {
    case QtDebugMsg:
        fprintf(flogfile, "%s\n", qPrintable(msg));
        break ;
    case QtInfoMsg:
        fprintf(flogfile, "%s\n", qPrintable(msg));
        break ;
    case QtWarningMsg:
        fprintf(flogfile, "WARNING: %s\n", qPrintable(msg));
        break ;
    case QtCriticalMsg:
        fprintf(flogfile, "CRITICAL: %s (%s)\n", qPrintable(msg), func);
        break ;
    case QtFatalMsg:
        fprintf(flogfile, "FATAL: %s (%s:%u, %s)\n", qPrintable(msg), file, context.line, func);
        break ;
    }
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    if ((flogfile = fopen("/home/user/llog", "a")) == nullptr) {
            flogfile = stderr;
            printf("can't open: %s", strerror(errno));
        }
    qInfo("suka");

    return a.exec();
}