understand passing parameters by reference with dynamic allocation

Question

I\'m trying understand how to pass a parameter by reference in C language. So I wrote this code to test the behavior of parameters passing:

#include 

        

Answer 1

You want to modify the value of n in main, not what n points to, so you need to pass a pointer to it. Since the type of n in main is int *, the parameter to alocar needs to be of type int **:

void alocar(int **n)
{
  *n = malloc(sizeof **n); // note no cast, operand of sizeof
  if (!*n)
    exit(-1);

  **n = 12;
  printf("%d\n", **n);
}

int main(void)
{
  int *n;
  alocar(&n);
  printf("%d\n", *n);  // we've already tested against n being NULL in alocar
  free(n);             // always clean up after yourself
  return 0;
}