How to Access CMake Variables from Within C Source Code?

Accessing CMake Variables within C Source Code

When working with CMake, it is often desirable to store project-wide information in centralized variables. This allows for easy management and accessibility. However, accessing these variables directly within C source code can be challenging.

CMake Variable Declaration

In the provided scenario, the CMake variable LIBINTERFACE_VERSION is defined to store the library's version number:

<code class="cmake">SET(LIBINTERFACE_VERSION 1 CACHE INTEGER "Version of libInterface")</code>

Accessing the Variable in C

To access LIBINTERFACE_VERSION in C , you can utilize one of two methods:

1. add_definitions

The add_definitions() function allows you to pass CMake variables as definitions to the compiler:

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

Within your C code, you can then access the variable as:

<code class="cpp">#include <version_config.h>
unsigned int version = VERSION_LIBINTERFACE;</version_config.h></code>

2. configure_file

You can also use configure_file() to create a header file template (e.g., version_config.h.in) where CMake variables are replaced:

<code class="cmake"># version_config.h.in
#ifndef VERSION_CONFIG_H
#define VERSION_CONFIG_H

// Define version_libinterface
#define VERSION_LIBINTERFACE @LIBINTERFACE_VERSION@
#endif // VERSION_CONFIG_H

configure_file( version_config.h.in ${CMAKE_BINARY_DIR}/generated/version_config.h )
include_directories( ${CMAKE_BINARY_DIR}/generated/ )</code>

Within your C code, you can then include the generated header file:

<code class="cpp">#include "version_config.h"
unsigned int version = VERSION_LIBINTERFACE;</code>

This approach provides additional flexibility for incorporating multiple defines or variables in your header file.

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