C macro trick for selective replace - c

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

As gcc-specific solution,
The `alias' attribute causes the declaration to be emitted as an
alias for another symbol, which must be specified. For instance,
void __f () { /* Do something. */; }
void f () __attribute__ ((weak, alias ("__f")));

Answer 2

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.

Answer 3

You could do something like this:
#define get_resolution __mock_get_resolution
somewhere globally accessible (like a header you always include etc.) and then do this:
#undef get_resolution
void get_resolution()
{
}
#define get_resolution __mock_get_resolution
void display()
{
get_resolution();
}
Ugly hack, but it will save you having to write a sed(1) script.
Test case follows:
$ gcc -o test test.c
$ ./test
__mock_up
$ cat test.c
#include <stdio.h>
#define get_resolution __mock_up
int
__mock_up()
{
printf("__mock_up\n");
}
#undef get_resolution
int
get_resolution()
{
}
#define get_resolution __mock_up
int main()
{
get_resolution();
return 0;
}
$