Question

How can I add an error to the perror stack?

here is an example of what I want

#include <stdio.h>
#include <stdlib.h>

int Div (int a, int b, int * c) {
   if (b == 0) {
       // add to perror: "cannot divide by zero!"
       return 0;
   }
   *c = a / b;
   return 1;
}

int main () {
   int n;
   if (!Div(2, 0, &n)) {
      perror("could not divide");
   }
   return 1;
}

Answer 1

There is no standard (or nonstandard, on the systems I’m aware of) way to add new errno values; you can assign to errno to use existing values, but this is not a good idea for anything not part of the standard library.