C do-while-0

do { ... } while (0) is a C idiom that executes a block exactly once while appearing syntactically like a loop. Compilers optimize it away completely, producing no extra machine code. It's commonly used in function macros to safely wrap multiple statements and enforce semicolon syntax.

Use do-while(0) in macros to enable safe statement grouping and prevent control flow issues.

This example shows do-while-0 wrapping multiple statements in a function macro.

// compile: gcc -o dowhile dowhile.c
// run: ./dowhile
// description: do-while-0 enables safe multi-statement function macros
 
#include <stdio.h>
 
#define LOG_ERROR(fmt, ...) do { \
    fprintf(stderr, "[ERROR] " fmt "\n", ##__VA_ARGS__); \
    perror("System error"); \
} while (0)
 
int main() {
    if (1) {
        LOG_ERROR("Failed to open file");
    }
 
    return 0;
}