Checking the return value of a function in a macro

Question

I have core function which i can call from the customized module of the product.

function_core is the core function which will return and integer we have a macro in header file

#define func_cust function_core

i am calling

func_cust inside my customized code.

EDIT: but inside the core we again call some other core function
 #define function_core main_core
so i cannot put in my customized code all the arguments.

i am calling this func_cust function call in many c files.

i need to check the return value of the function function_core like if function_core returns x then i want to change the return value to 0 or else same return value willl be returned.

for eg i want to define a macro like this

#define funct_cust ((function_core==x)?0:function_core)

Is this possible?

To be more specific this is what i need!!

#include<stdio.h>

#define sum_2 ((sum_1==11)?0:sum_1)
#define sum_1(a,b) sum(a,b)
int sum( int ,int);

int main()
{
int a,b,c;
a=5;
b=6;
c=sum_2(a,b);
printf("%d\n",c);
}

int sum(int x,int y)
{
return x+y;
}

this gives an error :

"test_fun.c", line 12.3: 1506-045 (S) Undeclared identifier sum_1.

i only have the access to play with this macro sum_2.

Answer 1

If you can add an actual function, it would be pretty easy:

int sanitize(int value, int x)
{
  return (value == x) ? 0 : value;
}

Then just change your macro into

#define func_cust sanitize(func_core(), x)

This solves the otherwise hairy problem of not evaluating the function call twice, and not having to introduce a temporary (which is hard to do in a macro).

If evaluating twice is okay, then of course just do it like you outlined:

#define func_cust  func_core() == x ? 0 : func_core()

Answer 2

It's better to write an inline function (C99 supports this):

static const int x = ...;
static inline int funct_cust(void* args) {
    int res = function_core(args);
    if (res == x) return 0;
    return res;
}

If you use gcc, you can use statement exprs:

#define funct_cust(args) ({ int res = function_core(args); res == x ? 0 : res; })