How to Access CMake Variables in C Source Code?

Accessing CMake Variables in C Source Code

Problem:
How can a CMake variable, such as LIBINTERFACE_VERSION, be accessed and used within C source code?

Answer:

Option 1: Using add_definitions

• Pass the CMake variable as a definition using add_definitions().

• Example:

  <code class="cmake">add_definitions( -DVERSION_LIBINTERFACE=${LIBINTERFACE_VERSION} )</code>

• This allows the CMake variable to be defined in the C code as a macro (#define).

Option 2: Using configure_file with header-file template

• Create a header-file template containing the CMake variable references.

• Example:

  <code class="cmake">// version_config.h.in
  #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</code>

• Use configure_file() to generate the header file replacing the CMake variables with their values.

• Example:

  <code class="cmake">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...</code>

• Include the generated header file in the C source code.

Example Usage:

<code class="cpp">// Assuming version_config.h is included
std::string version = VERSION_LIBINTERFACE;</code>

Note:
The configure_file() method is more extensible as it allows for additional variables or definitions to be added to the generated header file.

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