Why external Makefile not working in Qt project?

[OroszB]

I have a Qt Widget Application in Ubuntu.
I also have another project, which contains some .cpp files, this project has a Makefile.

This Makefile looks like this:

g++ -o Output main.cpp MyClass.h MyClass.cpp -std=c++11

I have a model layer in the Qt project, here I want to call the Makefile of another project like this:

QProcess process;
process.setWorkingDirectory("/path/to/my/another/project/");
process.setStandardErrorFile("/path/to/my/another/project/error.txt");
process.start("make");
process.waitForFinished();

When the process finished in the error.txt I got linking errors.
When I run this Makefile from terminal I got a proper output.

What should I set in Qt to be able to use make or g++ command inside the code without any linking error?
Which settings can ruin the compile or what should I change in my Qt project?

I tried it many ways:
create shell script when I call make command and process that script in Qt.
create shell script when I type the full g++ command and process that script in Qt.
I tried this:

process.start("sh", QStringList() << "-c" << "g++ -o Output main.cpp MyClass.h MyClass.cpp -std=c++11");

I used system function like this:

system("g++ -o Output main.cpp MyClass.h MyClass.cpp -std=c++11);

[JonB]

@OroszB
Whatever the issue is, your later alternative procss.start() or system() calls should not help/be relevant/necessary.

There is no reason why you should not be able to run a compilation/link elsewhere via QProcess.

When the process finished in the error.txt I got linking errors.

When I run this Makefile from terminal I got a proper output.

You should analyse why the other process produces link errors --- what is wrong/goes wrong --- when run from your app instead of from the command line. (You should also redirect standard output as well as error --- you never know when something might appear there.)

Purely at a guess: since you do seem to have set the working directory for the other process, which is good, are the environment variables the same when spawned from your first app/Qt Creator versus what they are set to when run from the command line?

[OroszB]

@JonB Which enviroment variables should I set in Qt? I know that exist the setProcessEnvironment() function, but I do not know what should I set with it.

[JonB]

@JonB said in Why external Makefile not working in Qt project?:

You should analyse why the other process produces link errors --- what is wrong/goes wrong --- when run from your app instead of from the command line. (You should also redirect standard output as well as error --- you never know when something might appear there.)

[OroszB]

I solved it, the makefile contains this command as well:

flex MyLanguage.l

and in the OS there is two intalled flex, Qt used the wrong one.