Question

Is there a macro trick to rename just the function calls without affecting the function definition, specifically for gcc/cpp:

#define get_resolution __mock_get_resolution

The above macro changes all places, but I just want this to take effect for the function call get_resolution(); without affecting the definition void get_resolution()

void get_resolution()
{
}

void display()
{
    get_resolution();
}

Answer 1

No, the C preprocessor has no semantic knowledge of the structure of the C program, it just sees text tokens.

One option would be to #undef the macro before the definition and redefine it afterwards, but this is messy. Another option would be to add a macro to the definition of each function you want to mock like this:

#if DO_MOCKING
#define IMPLEMENT_MOCKABLE_FUNCTION(funcname) _real_ ## funcname
#define get_resolution _mock_get_resolution
#else
#define IMPLEMENT_MOCKABLE_FUNCTION(funcname) funcname
#endif

...

void IMPLEMENT_MOCKABLE_FUNCTION(get_resolution)()
{
    ...
}

Also note that identifiers beginning with two underscores, as well as identifiers beginning with an underscore followed by a capital letter, are reserved by the implementation (i.e. the compiler and standard libraries). So I’ve renamed the identifiers in the example above to use a single underscore and a lowercase letter.