msbuild: set a specific preprocessor #define in the command line

Question

In a C++ file, I have a code like this:

#if ACTIVATE
#   pragma message( \"Activated\" )
#else
#   pragma message( \"Not Activated\")
#endif

I

Answer 1

If you need to define some constant (not just true/false), you can do it the following way:

On command line:

MSBuild /p:MyDefine=MyValue

In vcxproj file (in section ; and/or , depending on where you need it):

MY_DEFINE=$(MyDefine);$(PreprocessorDefinitions)

Note that if you don't specify /p:MyDefine=MyValue in a call to MSBuild then empty string will be assigned to MY_DEFINE macro. If it's OK for you, that's it. If not, keep reading.

How to make a macro undefined if corresponding MSBuild parameter is not specified

To have MY_DEFINE macro undefined instead of empty string, you can use the following trick:

  ....
  _DEBUG;_CONSOLE;OTHER_UNCONDITIONAL_MACROS;%(PreprocessorDefinitions)
  MY_DEFINE=$(MyDefine);%(PreprocessorDefinitions)
  ....

First PreprocessorDefinitions defines unconditional macros. Second PreprocessorDefinitions additionally defines MY_DEFINE macro when MyDefine is not empty string. You can test this by placing the following piece of code into your cpp file:

#define STRINGIZE2(x) #x
#define STRINGIZE(x) STRINGIZE2(x)

#ifndef MY_DEFINE
#pragma message("MY_DEFINE is not defined.")
#else
#pragma message("MY_DEFINE is defined to: [" STRINGIZE(MY_DEFINE) "]")
#endif

and running:

> MSBuild SandBox.sln /p:Configuration=Debug /p:MyDefine=test /t:Rebuild
...
MY_DEFINE is defined to: [test]
...

> MSBuild SandBox.sln /p:Configuration=Debug /p:MyDefine= /t:Rebuild
...
MY_DEFINE is not defined.
...

> MSBuild SandBox.sln /p:Configuration=Debug /t:Rebuild
...
MY_DEFINE is not defined.
...