#include <stdio.h>
#define FILENAME "test.txt"
#define N 20
int main()
{
  FILE *fp;
  char buffer[N];
  fp = fopen(FILENAME, "r");
  if (fp == NULL) {
    fprintf(stderr, "cannot open the file %s.", FILENAME);
    return -1;
  }
  fgets(buffer, N, fp);
  printf("%s", buffer);
  fclose(fp);
  return 0;
}
/* end */

cannot open the file test.txt.
Exited: ExitFailure 255