Question

I have macro like this:

#define error_exit(format, ...) \
    error_at_line(EXIT_FAILURE, 0, __FILE__, __LINE__, format, ##__VA_ARGS__)

that I use to as a general fatal error function. Unfortunately, error_at_line doesn’t have the noreturn gcc attribute because if you specify 0 as the first argument it does return. This causes problems, specifically, I get uninitialized variable warnings because gcc can’t figure out that error_exit will never return.

For example:

int x;
switch(...) {
    case VALID:
        x = 1;
        break;
    default:
        error_exit(...);
}
return x;

gives me warning. So, how can I go about apply noreturn to a macro or even specific function invocation?

Answer 1

Assuming GCC ≥ 4.5.0,

#define error_exit(format, ...) \
    do { \
        error_at_line(EXIT_FAILURE, 0, __FILE__, __LINE__, format, ##__VA_ARGS__); \
        __builtin_unreachable(); \
    } while (0)