类似于函数的宏，与类似对象的宏同名

Question

Is it possible to have in C something like:

#define MACRO_EX 333

#define MACRO_EX(X,Y) ((X) < (Y) ? : (X) : (Y))

Can they coexist?

Answer 1

The C standard says (ISO/IEC 9899:1999, §6.10.3, 2):

An identifier currently defined as an object-like macro shall not be redefined by another #define preprocessing directive unless the second definition is an object-like macro definition and the two replacement lists are identical. Likewise, an identifier currently defined as a function-like macro shall not be redefined by another #define preprocessing directive unless the second definition is a function-like macro definition that has the same number and spelling of parameters, and the two replacement lists are identical.

So the answer is no.

Answer 2

No. A function-like (with args) and an object-like macro (no args) can not be defined with the same name (in standardese, attempting to do so violates a shall not rule, which means the compiler is required to diagnose it). However, C99 specifies variadic macros (taking 1 or more args). Maybe that'll do what you want?

You are free to #undef MACRO_EX and redefine it with args, if that solves your problem. But it can be used only with or without args.

Answer 3

warning: "MACRO_EX" redefined [enabled by default]

In this program,

    #include <stdio.h>
    #include <stdlib.h>

    #define MACRO_EX 333
    #define MACRO_EX(X,Y) ((X) < (Y) ? : (X) : (Y))

    int main()
    {

    printf("\n %d  %d\n", MACRO_EX, MACRO_EX(10,20));
    printf("\n %d  %d\n", MACRO_EX);

    return 0;
    }

Im getting

 warning: "MACRO_EX" redefined [enabled by default]
 note: this is the location of the previous definition
 In function ‘main’:
 error: ‘MACRO_EX’ undeclared (first use in this function)
 note: each undeclared identifier is reported only once for each function it appears in
 error: expected ‘)’ before ‘:’ token

If I comment one macro & it's usage then works fine :)

But As per C99 Std

6.10.3

An identifier currently defined as an object-like macro shall not be redefined by another #define pre-processing directive unless the second definition is an object-like macro definition and the two replacement lists are identical. Likewise, an identifier currently defined as a function-like macro shall not be redefined by another #define pre-processing directive unless the second definition is a function-like macro definition that has the same number and spelling of parameters, and the two replacement lists are identical.

I tried the same code by compiling with -std=c99 still getting same error.

Answer 4

see

http://codepad.org/0nfvOGTl

#include<stdio.h>
#define MACRO_EX 333

#define MACRO_EX(X,Y) ((X) < (Y) ? : (X) : (Y))


int main()
{

printf("valud is %d",MACRO_EX);
return 0;
}

error

Line 0: warning: "MACRO_EX" redefined
Line 0: warning: this is the location of the previous definition
In function 'main':
Line 10: error: 'MACRO_EX' undeclared (first use in this function)
Line 10: error: (Each undeclared identifier is reported only once
Line 10: error: for each function it appears in.)