How to read a CMake Variable in C++ source code

Question

I'd like to store the version number of my library in just one place. So I have defined such a variable in the CMake-file:

    SET(LIBINTERFACE_VERSION 1 CACHE INTEGER "Version of libInterface")

With this definition I can generate a version.rc file according to Microsoft's definition, which I compile into the library and afterwards shows up correctly in the properties window of my dll-file.

Now I'd like to use this CMake variable in my c++ source code too, but I actually don't get to a working solution. I've tried different things like this:

    #ifndef VERSION_LIBINTERFACE
    #  define VERSION_LIBINTERFACE @LIBINTERFACE_VERSION@
    #endif

or this:

    unsigned int getLibInterfaceVersion()
    {
        return @LIBINTERFACE_VERSION@;
    }

But the compiler won't accept anything. Since my researches in the CMake-Documentation didn't get any results, I hope that someone could give me the essential advice.

Thanks in advance.

You need to pass this variable value to compiler as precompiler constant. Exact syntax depends on compiler used. — Alex F
– Alex F, Commented Oct 26, 2011 at 9:10
I'm using the Visual Studio 2010 Compiler. So I can use it like the constants listed in msdn.microsoft.com/en-us/library/b0084kay(v=vs.80).aspx? Can you give me an example? — Snowfox
– Snowfox, Commented Oct 26, 2011 at 9:27

waldyrious · Accepted Answer · 2016-04-19 15:16:55Z

100

The easiest way to do this, is to pass the LIBINTERFACE_VERSION as a definition with add_definition:

add_definitions( -DVERSION_LIBINTERFACE=${LIBINTERFACE_VERSION} )

However, you can also create a "header-file template" and use configure_file. This way, CMake will replace your @LIBINTERFACE_VERSION@. This is also a little more extensible because you can easily add extra defines or variables here...

E.g. create a file "version_config.h.in", looking like this:

#ifndef VERSION_CONFIG_H
#define VERSION_CONFIG_H

// define your version_libinterface
#define VERSION_LIBINTERFACE @LIBINTERFACE_VERSION@

// alternatively you could add your global method getLibInterfaceVersion here
unsigned int getLibInterfaceVersion()
{
    return @LIBINTERFACE_VERSION@;
}

#endif // VERSION_CONFIG_H

Then add a configure_file line to your cmakelists.txt:

configure_file( version_config.h.in ${CMAKE_BINARY_DIR}/generated/version_config.h )
include_directories( ${CMAKE_BINARY_DIR}/generated/ ) # Make sure it can be included...

And of course, make sure the correct version_config.h is included in your source-files.

edited Apr 19, 2016 at 15:16

waldyrious

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answered Oct 26, 2011 at 9:27

André

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3 Comments

frankliuao Over a year ago

add_definitions is probably easier

André Over a year ago

@frankliuao. Agreed, that's why it is the first sentence of my answer.

jaques-sam Over a year ago

This is then passed to all targets, better to use target_compile_definitions

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