Convert QFile to FILE*

Question

Is there another way to convet QFile to File? Different than this:

QFile myFile("goforward.raw");
int FileDescriptor = myFile.handle();
FILE* fh = fdopen(FileDescriptor, "rb");

Answer 1

We had very strange problems with our application and finally traced it to the QFile/fdopen issue:

void foo(QString filename)
{
    QFile qf(filename);
    qf.open(QIODevice::ReadOnly);
    int fd = qf.handle();
    FILE* f = fdopen(fd, "rb");
    // do some stuff with f
    fclose(f); // !!! undefined behaviour !!!
}

The problem with this code is that fclose(f) is called before the QFile object is destroyed, which is the wrong order: QTBUG-20372

...so either destroy the QFile object before calling fclose() or duplicate the file descriptor returned by QFile::handle():

void foo(QString filename)
{
    QFile qf(filename);
    qf.open(QIODevice::ReadOnly);
    int fd = qf.handle();
    FILE* f = fdopen(dup(fd), "rb"); // !!! use dup()
    // do some stuff with f
    fclose(f); // correct
}

P.S.: Those strange problems with our app showed up only on very few systems by a 10 second delay between a return statement at the end of a function and the actual return from that function. It was really weird. So this is an example of an "undefined behaviour" manifested in the real world :o)