HEARD OF TARGETS?

Qmake uses ‘targets’, thet’re like modules which you define, and insert into the main build chain, telling the resulting Makefile when to build what. Targets can be auto-executed, or simply residing in your make file, so that you can build them on demand.

Here is a simple example, covering the external_library.a story above.
In your main .pro file, add these lines:

extralib.target = extra
extralib.commands =	echo "Building extralib.."; \
				make -w -C ../my_libraries/extralib; \
				echo "Done building extralib."; \
extralib.depends =
QMAKE_EXTRA_TARGETS += extralib
PRE_TARGETDEPS = extra

.. the rest of your .pro file comes here ..
}

From now on, when building your main project, it will automatically try to build the extralib project. This step will be executed before the linker requests the resulting extralib.a, that way you will always have a consistent build.

But you can do much more with targets, you can for example set up doxygen to automatically export new docs on rebuilds, or to copy files, add text to your files – svn revision number maybe, or else.

If you leave out the PRE_TARGETDEPS = extra, the extralib target you defined will not be automatically execute during builds. But you will be able to type in your shell:

$ make extra

.. which will execute this specific target.

Additionally, if one of your targets depends on other target(s), you just need to add them to the ‘extralib.depends =’ variable. Note that you can execute a shell script via targets, in case you need to do complex file operation, which would be too painful to write in the .pro file, or which depend on external shell scripts.