CMake command line for C++ #define

Question

I need to compile different versions of a certain project by adding compiler switches. Usually I would do this by using add_definitions or something like

set_property( TARGET mylib PROPERTY COMPILE_DEFINITIONS _MYDEFINE=1 ) 

in the CMakeLists.txt file.

In this specific project however, I am not allowed to modify any sources, including the CMakeLists.txt file.

I was hoping that something like

cmake -D_MYDEFINE=1 <path to sources> 

would generate a project file (Visual Studio 2008 in my case, but shouldn't matter) which includes _MYDEFINE=1 in its preprocessor definitions but in fact it won't.

What are my options here? Is there a different cmake command line option to achieve this? Feel free to suggest solutions not including the command line, as long as changing the project's CMakeLists.txt is not necessary.

Answer 1

I managed to do it this way now:

I was able to convince everybody to add the following lines to the common CMakeLists.txt:

IF (NOT DEFINED _MYDEFINE)     SET(_MYDEFINE <default value>) ENDIF() ADD_DEFINITIONS(-D_MYDEFINE=${_MYDEFINE}) 

(No it is not really called "MYDEFINE", and <default value> is just a placeholder, I just replaced all that for this example)

This does not change the current behaviour of compiling with no additional compiler flags and is thus a valid change.

And it allows you to do

cmake -D_MYDEFINE=<my value> <path to sources> 

where this cmake definition will be mapped to a C++ precompiler definition when cmake creates the project file.