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.

`cmake -DCMAKE_CXX_FLAGS="-D_MYDEFINE=1" ` – user362515 Sep 11 '21 at 10:35 — user362515, Sep 11 '21 at 10:35

score 30 · Accepted Answer · answered Mar 02 '12 at 13:01

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.

Instead of conditional setting of `_MYDEFINE` variable it is better to set CACHE variable: `SET(_MYDEFINE CACHE STRING "Additional definition" )`. This reflects the meaning of the variable: **user-provided parameter**. — Tsyvarev, Jul 17 '21 at 09:41

Naszta · Answer 2 · 2012-03-02T16:37:12.417

11

Container CMakeLists.txt solution

Tricky solution:

Your read only CMakeList.txt path: ${path}/ReadOnlyProject/CMakeLists.txt

Create a new CMakeList.txt to upper to the read only library (${path}/CMakeLists.txt):

CMAKE_MINIMUM_REQUIRED(VERSION 2.8.0)
PROJECT (FAKE_PROJECT)

ADD_DEFINITIONS(-D_MYDEFINE=1)

ADD_SUBDIRECTORY(ReadOnlyProject)

Now use your new project (FAKE_PROJECT) to compile. If the ReadOnlyProject does not set compilers definitions directly, it could work.

On Visual Studio 2010:

Try to modify c:\Users\${username}\AppData\Local\Microsoft\MSBuild\v4.0\Microsoft.Cpp.Win32.user.props to add custom compiler settings.

You should add the followings:

<Project>
  ...
  <ItemDefinitionGroup>
    <ClCompile>
      <PreprocessorDefinitions>__MYDEFINE=1;%(PreprocessorDefinitions)</PreprocessorDefinitions>
    </ClCompile>
  </ItemDefinitionGroup>
</Project>

edited Mar 02 '12 at 16:37

answered Mar 02 '12 at 10:32

Naszta

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Hm my %APPDATA%\Microsoft folder doesn't have any MSBuild folder (I'm on Windows XP btw) – Tim Meyer Mar 02 '12 at 10:37
Ok, I am using Visual Studio 2010. I will look for 2008 settings. – Naszta Mar 02 '12 at 10:47
+1 for Microsoft.Cpp.Win32.user.props update, needed to add prepocessor directive without changing .vcxproj – watbywbarif Nov 11 '14 at 15:32
The Container CMakeLists.txt solution seems not working with projects using CMAKE_SOURCE_DIR. – ZHANG Zikai Sep 14 '16 at 03:43

score 6 · Answer 3 · answered Sep 20 '18 at 13:40

To pass a C++ or C pre-processor define without modifying any CMake source files, use the environment variables CFLAGS for C or CXXFLAGS for C++ respectively, e.g.:

$ export CXXFLAGS="-D_MY_DEFINE=1 -D_MY_OTHER_DEFINE=1"
$ mkdir build
$ cd build
$ cmake ..

CMake command line for C++ #define

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