Optional assertion description argument

assert.c

#include <stdio.h>

static inline void _AssertionFailed(char *expr, char *reason)
{
    if (!reason || *reason == '\0')
        printf("Assertion failed: %s\n", expr);
    else
        printf("Assertion failed: %s (Reason: %s)\n", expr, reason);
}

#define ASSERTN(expr, ...) _AssertionFailed(#expr, "" __VA_ARGS__)
#define ASSERT(...) ASSERTN(__VA_ARGS__)

int main(int argc, char **argv) {
    // Without a reason:
    ASSERT(0);

    // With a reason:
    ASSERT(0, "Should not get here");

    return 0;
}