Check if regex is a valid POSIX Extended regex

regex.c

#include <stdio.h>
#include <regex.h>

int main(void) {
	char pattern[256];
	scanf("%s", pattern);
	regex_t regex;
	const int errcode = regcomp(&regex, (const char *)pattern, REG_EXTENDED);
	if(errcode == 0) {
		printf("regex valid\n");
		return 0;
	}
	char errbuf[256];
	regerror(errcode, &regex, errbuf, sizeof(errbuf) / sizeof(char));
	printf("%s\n", errbuf);
	return errcode;
}