[SOLVED] How to define a C++ preprocessor macro through the command line with CMake?

Issue

I try to set a preprocessor macro in the command line of CMake. I've tried:

set generator="Visual Studio 8 2005"
set params=-D MY_MACRO=1
cmake.exe -G %generator% %params% ..\some_project

but it's neither defined when I compile nor can I find the name MY_MACRO in the files generated by CMake at all, except for CMakeCache.txt where it's present in the form:

MY_MACRO:UNINITIALIZED=1

How can I do it?

Solution

The motivation behind the question was to batch build 3rd party libraries, which is why I wanted to avoid modifying CMakeLists. So years later, even though I don't need that anymore, I figured out that it's easily achievable by means external to CMake:

• Invoke CMake as usual, no special flags.

• Then:

  • With MSVC: The compiler reads the CL environment variable to get extra command line arguments. So

      set CL=/DMY_MACRO=1 %CL%
    

    then invoke MSBuild to do its job.

  • With Makefiles: The generated makefiles use the CFLAGS and CXX_FLAGS variables as makefiles are expected to do. So the build can be started by

      make CXX_FLAGS=-DMY_MACRO=1
    

    or by setting the corresponding environment variables.

Answered By - Yakov Galka

Answer Checked By - Clifford M. (WPSolving Volunteer)