从外部Qt运行时Qt5应用程序崩溃

Question

I have a strange issue that appeared only recently.

When I acces an external binary from inside my Qt app, the app crashes with the error:

Exception Type:  EXC_CRASH (SIGABRT)

But when I run it from the "build and run" inside Qt Creator, everything runs fine when I acces the point in my application where I hit an exetrnal binary.

This is the function I hit when the app crashes from outside Qt creator

QString Api::getVideoFrame(QString filename, QString position)
{
    const QString ffmpeg = QDir::currentPath()+"/ffmpeg"; //mac version
    QProcess process;
    QStringList args;
    args    << "-ss" << position
            << "-i" << filename
            << "-f" << "image2"
            << "-vframes" << "1"
            //<< "-vcodec" << "bmp"
            << "pipe:1";
    process.start(ffmpeg, args);
    process.waitForFinished();

    return QString(process.readAllStandardOutput().toBase64());
}

It also crashes when accessing other external binaries, not only ffmpeg in this case.

I have the feeling it has something to do with the QDir::currentPath() because when I mess up the path, It also crashes from inside Qt Creator.

obviously I added the corresponding binaries next to the executable file in the Contents/MacOS/ folder

I don't really know how to debug this.. any clue how to solve this?

Answer 1

I actually found out why this happens and it is quite interresting to note that

QDir::currentPath()

has to be used with care on mac osX.

When an app is executed from within Qt Creator it returns :

/Volumes/LSPRO/Build/LSPRO.app/Contents/MacOS

including the path to te binary inside the .app package

But when you run it as a standalone app, it returns

/Volumes/LSPRO/Build

At least on my configuration...

Answer 2

I don't really know how to debug this.. any clue how to solve this?

Yes, I have some clue.

You could try using QCoreApplication::applicationDirPath() for this scenario to get this working properly on MAC as also asserted by a user in the comment.

Here you can find the filesystem engine source code though if you wanna further track the issue down with your suspect as a bug. In short, there is not much Mac specific code in there rather than Unix.

Also, in the future you may wanna consider QtMultimedia rather than dealing with QProcess and external execution.