Can you make a VC++ Solution set preprocessor #defines on loaded projects?

Question

I have a library which supports a #define to control how it's built. However the library can be used by multiple EXE projects which want different versions. Can I make the app/EXE project set the #define to be used by the library when built, or set it in the solution?

The only other option I can think of is creating a separate build-configuration on the library project but that would quickly get out of control. That's common for e.g unicode/non-unicode builds but then you'd end up multiplying the number of configurations for every combination.

Answer 1

The following approach assumes that every .EXE/app (which uses this library) has its own Visual Studio Solution.

You do have control over the library, right? Steps 1-3 will make changes to its project file, and step 4 adds a file to the library source code.

1. Set Project Properties > C/C++ > Advanced > Force Includes to mylibrary_solution_defines.h .

2. Edit Project Properties > C/C++ > General > Additional Include Directories to put $(SolutionDir); at the beginning of the list of directories.

3. Set both Project Properties > General > Output Directory and Intermediate Directory to something relative to the solution directory. Perhaps $(SolutionDir)$(ProjectName)\$(Configuration)? You want to make sure the library gets rebuilt for every solution that uses it; there shouldn't be any sharing of .lib or .obj files.

4. Create an empty, dummy header file called mylibrary_solution_defines.h and put it in your library source code so a #include "mylibrary_solution_defines.h" will never fail.

5. In every app/EXE solution -- assuming you have different solutions for each app that uses this library, otherwise this whole plan will fail -- create a mylibrary_solution_defines.h file with your #defines in it.

Do you see what's happening? Every library source file implicitly #includes "mylibrary_solution_defines.h", and it preferentially gets that file from the solution directory. So that file can be different for every solution. So if your solution ConsoleModeInterfaceProgram.sln needs the library built with #define TEXTONLY 1, put that line into the mylibrary_solution_defines.h that's in the same directory as ConsoleModeInterfaceProgram.sln.