Question

Sometimes when I change code in my Qt project (Qt Creator 2.1.0 with mingw32), the changes don’t get reflected in the produced machine code after building it. This happens mostly when I change things like default values in constructors or the order of parameters in methods/constructors. Usually, a full rebuild fixes that (but takes a few minutes).

I’m helping myself by deleting the generated executables or librarys before building, which seems to help most of the time. Does that mean that theres something going wrong when linking the object files?

I’m coming from java/.net and I’m used to a different behaviour. I’d be happy if anyone could explain me what I’m doing wrong and/or point me to some related articles.

Thank you!

Answer 1

Usually, after a change in a header, all source files including that header should be rebuilt.
However, qmake is a bit peculiar in this regard, you need to set DEPENDPATH for include folders other than the current directory. E.g., if you have

INCLUDEPATH += somepath_in_my_project

also add

DEPENDPATH += some_path_in_my_project

Only with DEPENDPATH, files built by the .pro files are rebuilt if some header in some_path_in_my_project changes (if they include that header)!

I suggest to add for each INCLUDEPATH line an identical DEPENDPATH line, unless you include some system directory you don’t expect to change.

Edit:

A similar problem exists when linking statically with qmake: If the static lib foo.a changes, binaries linking against it are not relinked. That’s a bug in QMake, not generating the correct dependencies.

A workaround I found in a former project:

static:unix:TARGETDEPS += path_to_my/somestaticlib.a
static:win32:TARGETDEPS += path_to_my/somestaticlib.lib

Edit edit:

Since some time (Qt 5?), above code should use POST_TARGETDEPS instead of TARGETDEPS.