Maybe SUBDIRS project will help you?

But i need to have only one .a file like output.
SUBDIR can do it, if yes, how?

Then I didn’t understand your question clearly. As I understood you have library project (that generates .a after building) and another project that uses this library.

What I’d like to do is:
Have a Project (static lib) named “ABC”, this project don’t have file .h or cpp inside but have other 3 project: “A” “B” “C”.
I hope to have done clear.
Thanks.

So your static lib project collects all the object files of the three projects A, B and C and combines them to one static lib?

Yes, this because i can have also the need to have only one lib, for example “libA.a”, even to have all “libABC.a”. I’d like to have the possibility to compile or a different solution “A” “B” etc… or a single solution “ABC”.
Thanks.

You’ll need different configuration switches in QMake then, like this:

!altogether:SUBDIRS=A B C
altogether:SUBDIRS=A

and in the altogether case have A.pro also compile and link the files from B and C

then run qmake with CONFIG+=altogether or CONFIG-=altogether

I’m not able to understand, could you please send me an example or post a link with it.
My email address is cervelli.leonardo@gmail.com
Thanks and sorry.