- (void) string_format(name, 4, "%c%d", (index < 10 ? 'c' : 'm'), index);
+ if (index < 10)
+ (void) string_format(name, sizeof(name), "%c%d", 'c', index);
+ else if (index < 20) /* ignore out-of-range index */
+ (void) string_format(name, sizeof(name), "%c%d", 'm', index - 10);