getErrnoString.c

#include <stdio.h>
#include <string.h>
int main(int argc,char *argv[])
{
	if (argc < 2){
		printf("[Usage]: errno 2\n");
		return -1;
	}
	int err = atoi(argv[1]);
	printf("errno.%02d is %s\n",err,strerror(err));
	return 0;
}

gcc getErrnoString.c -o err
./err 12