qt - Qmake project dependencies (linked libraries)

Question

I have a project that links to a number of shared libraries.

Lets say project A depends on projects B and C

Ideally, I want to impose the following dependencies in my project file:

1. Rebuild project A if either B or C has been rebuilt since last time project A was built
2. Use the output for the relevant configuration (i.e. if building project A in debug mode, then use the debug versions of the libs for project B and C)

Does anyone know how I may explicitly express such dependencies in my project file?

Answer 1

After quite a bit of frustration with qmake, I have found what I think is the answer to your question. If not, then I have learned the way that I will use qmake until I find something better, because this is still a little bit ugly. I set up a demo project, this is my directory structure (files have extensions, folders do not):

MyProj
    MyProj.pro
    myproj-core
        myproj-core.pro
        globals.h
        MyProjCore.h
        MyProjCore.cpp
    myproj-app
        myproj-app.pro
        main.cpp

We start with MyProj.pro as a subdirs project, which is the key to doing what you ask. Basically, instead of depending on other projects to specify debug/release and all sorts of other junk, you just set it on the one qmake file. It doesn't let you make only what you need, but it's the best solution I could come up with. Here are the contents:

TEMPLATE = subdirs
# Needed to ensure that things are built right, which you have to do yourself :(
CONFIG += ordered

# All the projects in your application are sub-projects of your solution
SUBDIRS = myproj-core 
          myproj-app

# Use .depends to specify that a project depends on another.
myproj-app.depends = myproj-core

myproj-core.pro is your typical shared object library:

QT -= gui
TARGET = myproj-core
TEMPLATE = lib
DEFINES += MYPROJCORE_LIBRARY
SOURCES += MyProjCore.cpp
HEADERS += MyProjCore.h 
           globals.h

myproj-app.pro is consumer application, where the little rebuild-when-needed trick is:

QT       -= gui

TARGET = myproj-app
CONFIG   += console
CONFIG   -= app_bundle

TEMPLATE = app

# Specify that we're lookin in myproj-core.  Realistically, this should be put
# in some configuration file
INCLUDEPATH += ../myproj-core
# Link to the library generated by the project.  Could use variables or
# something here to make it more bulletproof
LIBS += ../myproj-core/libmyproj-core.so
# Specify that we depend on the library (which, logically would be implicit from
# the fact that we are linking to it)
PRE_TARGETDEPS += ../myproj-core/libmyproj-core.so

SOURCES += main.cpp

I hope this solves your problem, as I know it solved mine!

EDIT: I made a file specifically for building the dependencies for me, I store it in a sibling folder of each of my projects (child of the MyProj in the directory structure specified above) called dependencies.pri:

# On windows, a shared object is a .dll
win32: SONAME=dll
else:  SONAME=so

# This function sets up the dependencies for libraries that are built with
# this project.  Specify the libraries you need to depend on in the variable
# DEPENDENCY_LIBRARIES and this will add
for(dep, DEPENDENCY_LIBRARIES) {
    #message($$TARGET depends on $$dep ($${DESTDIR}/$${dep}.$${SONAME}))
    LIBS += $${DESTDIR}/lib$${dep}.$${SONAME}
    PRE_TARGETDEPS += $${DESTDIR}/lib$${dep}.$${SONAME}
}

So at the bottom of all the consuming applications, I can add the lines:

DEPENDENCY_LIBRARIES = myproj-core

include(../config/dependencies.pri)

This assumes that you are copying the libraries to some shared location and/or moving them around as needed, so my function might not work for you, but I figured I would add it to the solution.