using #defines and passing functions to them - c

Question

gcc 4.4.2 c89
I re-engineering some code in c89. However, I am totally confused with the code that uses the following #defines. So I created a small application that maybe I would understand more of how this is working.
From what I can gather the MODULE_API will pass a function name and call the macro MODULE_SOURCE_API and concatenate name and func. So I create a simple function called print_name and ran the code. I got the following error messages:
implicit declaration of function ‘print_name’
undefined reference to `print_name'
What would be the main reason for doing this?
#include <stdio.h>
#define MODULE_SOURCE_API(name, func) name##_##func
#define MODULE_API(func) MODULE_SOURCE_API(mod_print, func)
void MODULE_API(print_name)(const char const *name);
int main(void)
{
printf("=== Start program ===\n");
print_name("Joe bloggs");
printf("== End of program ===\n");
return 0;
}
void MODULE_API(print_name)(const char const *name)
{
printf("My name is [ %s ]\n", name);
}
Many thanks for any advice,
EDIT ====
I have just made a correction I should be calling
MODULE_API(print_name)("Joe Bloggs");
But how can I print out what will be the outcome of concatenating? And what is the reason for doing this?
Many thanks,

Answer 1

#define MODULE_SOURCE_API(name, func) name##_##func
#define MODULE_API(func) MODULE_SOURCE_API(mod_print, func)
void MODULE_API(print_name)(const char const *name);
That will be producing a function named mod_print_print_name instead of print_name
You can check it on gcc with the -E option.
gcc -E ak.c gives
/* ...... */
void mod_print_print_name(const char const *name);
int main(void)
{
printf("=== Start program ===\n");
print_name("Joe bloggs");
printf("== End of program ===\n");
return 0;
}
void mod_print_print_name(const char const *name)
{
printf("My name is [ %s ]\n", name);
}

Answer 2

You can try to manually expand the macros to understand what is going on:
void MODULE_API( print_name )( const char * name ); // the second const there is redundant
// maybe you meant 'const char * const??
=(expand MODULE_API)=>
void MODULE_SOURCE_API( mod_print, print_name )( const char* name );
=(expand MODULE_SOURCE_API)=>
void mod_print_print_name( const char *);
As you see, the function being declared (and defined at the end of the code) is not print_name, but rather mod_print_print_name. Go back to the initial code and see how the macro is intended to be used. I would assume that function calls are performed with the same macros that are used for declarations and definitions.