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?
If you are using CMake 3. X your first choice for adding a preprocessor macro should be target_compile_definitions. The reason you should prefer this approach over any other approach is because it granularity is target based. IE the macro will only be added to your exe/library.
You can use the command line to set entries in the Cache with the syntax cmake -D var:type=value , just cmake -D var=value or with cmake -C CMakeInitialCache. cmake .
Add -D define flags to the compilation of source files. Adds definitions to the compiler command line for targets in the current directory, whether added before or after this command is invoked, and for the ones in sub-directories added after.
The C preprocessor is a macro processor that is used automatically by the C compiler to transform your program before actual compilation. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs.
A good alternative would be to define a cmake option:
OPTION(DEFINE_MACRO "Option description" ON) # Enabled by default
Followed by a condition:
IF(DEFINE_MACRO)
ADD_DEFINITIONS(-DMACRO)
ENDIF(DEFINE_MACRO)
Then you can turn that option ON/OFF via command line with cmake using the -D
flag. Example:
cmake -DDEFINE_MACRO=OFF ..
To make sure the compiler is receiving the definition right, you can call make in verbose mode and check for the macro being defined or not:
make VERBOSE=1
This is a good solution also because make
will recompile your code when any of cmake options changes.
Try this: -D CMAKE_CXX_FLAGS=/DMY_MACRO=1
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.
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