Function macro is a preprocessor macro that looks and behaves like a function call. Arguments must be wrapped in parentheses to preserve precedence during substitution. Multi-statement function macros should use do { ... } while (0) to ensure proper scoping and require semicolon syntax.

Always parenthesize macro arguments to avoid operator precedence bugs.

This example demonstrates function macros with proper argument protection and multi-statement wrapping.

// compile: gcc -o funcmacro funcmacro.c
// run: ./funcmacro
// description: function macros look like functions but substitute inline
 
#include <stdio.h>
 
#define MAX(a, b) ((a) > (b) ? (a) : (b))
 
#define PRINT_PAIR(x, y) do { \
    printf("Values: %d, %d\n", (x), (y)); \
    printf("Max: %d\n", MAX((x), (y))); \
} while (0)
 
int main() {
    int x = 5, y = 3;
    PRINT_PAIR(x, y);
 
    int z = MAX(2 + 3, 4 + 1);  // correct: (2+3) and (4+1), not 2+3 and 4+1
    printf("Result: %d\n", z);
 
    return 0;
}