Is it safe to pass a void pointer to function that accepts a non-void pointer?

Question

Very simply, is the following code safe/portable?

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

int add(int *a, int *b)
{
  return *a + *b;
}

int main()
{
  int x = 2;
  int y = 3;

  void *ptr1 = &x;
  void *ptr2 = &y;

  fprintf(stdout, "%d + %d = %d\n", x, y, add(ptr1, ptr2));

  return EXIT_SUCCESS;
}

I've compiled this with -Wall -Werror and -Wextra and received no warnings; it seems to run fine.

Answer 1

There's two things to consider:

1. C allows the implicit conversion from a void pointer to any other object pointer type. So it's syntactically okay to pass those arguments.

2. The type of the actual object being pointed to, and the type of the pointer the function expects, must satisfy strict aliasing constraints, otherwise your program is in undefined behavior land.

You are okay on both points. So your program is perfectly fine.