#include <stdio.h>
#include <errno.h>
#include <string.h<
extern int errno ;
int main () {
FILE * pf;
int errnum;
pf = fopen ("unexist.txt", "rb");
if (pf == NULL) {
errnum = errno;
fprintf(stderr, "Value of errno: %d\n", errno);
perror("Error printed by perror");
fprintf(stderr, "Error opening file: %s\n", strerror( errnum ));
} else {
fclose (pf);
}
return 0;
}