perror

    void perror(const char *str);

Prints str (if non-null) and strerror(errno) to standard error as would:

fprintf(stderr, "%s: %s\n", (s != NULL ? s : ""), strerror(errno))

/* 
 * perror example code
 * http://code-reference.com/c/stdio.h/perror 
 */
 
#include <stdio.h> /* including standard library */
//#include <windows.h> /* uncomment this for Windows */
 
 
int main ( void )
{
FILE *stream;
 
stream = fopen("test_not_exists.txt","r");
 
if (stream == 0) {
perror("Here comes the perror code ->");
return 1;
}
 
printf("its all fine\n");
 
fclose (stream);
return 0;
 
}

 ./perror 
  Here comes the perror code ->: No such file or directory