QtCreator build returns collect2: ld returned exit

Question

While building several different projects in QtCreator, I have run across the following build error:

collect2: ld returned 1 exit status

After only changing a few things (that should not change anything significant in the build), it will go away if it has already appeared, or it will appear if it's not there.

In my current program for a school project, I am trying to compile rock03.cpp. It's the only file in the build, and has the main() method. I had just run it successfully, and went back to change the order of some if()s, now, I get only two relevant warnings:

overriding commands for target 'rock03.o'

and

ignoring old commands for target 'rock03.o'

along with the error in question.

Does anyone know why this would happen? I cannot seem to reproduce the error with any reasonable certainty, and QtCreator is not complaining about any thing before I build.

Thanks

Answer 1

The compiler output is really helpful if you're just getting this as an error, but the first candidate is probably that you've still got the output program open, and it can't write to the file, because that'll give you a solitary collect2 error like this

Answer 2

This happens when you do not close your main app (so the output executable is still running, but without any visible window). An example:

int main() {
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

This app ends fine when you close the main window, but this code

int main() {
    QApplication a(argc, argv);
    QDialog w;
    w.exec();
    return a.exec();
}

doesn't close the app when you close the dialog (at least for me).

A solution is to create always your main window and make sure you close it.

Answer 3

In my case, folder permissions were the problem. Checking the "Compile Output" window is crucial for finding out what exactly the problem is. (QtCreator is the opposite of Visual Studio in that regard, so it takes some getting used to.) I tried setting the permissions properly, but after that didn't seem to work, in the end I deactivated shadow build and then I went to "Tools/Options/Build&Run/General/Projects Directory" and set "Directory" to ".". Then it finally compiled. "It" being the kmap2qmap project in Qt 5.11.

Just my 2 cents in case anyone might find them useful.

Answer 4

There could be many more reasons for the error. But for me, on removing of unused SLOTS from the class the problem was solved.

Answer 5

Checking the "Compile Output" pane reveals that the .pro file was trying to link the same .cpp file twice.

Answer 6

If the only message error is this one concerning linker, the reason can be that your program is still running and linker can not access to the binary file. Be sure your application was stopped or kill it if still running. Qtcreator never checks if previous run was stopped before compiling.