Modify arrays inside functions in C. This subject is always tricky and I tend to forget, so here is a not to self.

array_pass_by_ref.c

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

/* demonstrate pass by reference of an array of integers*/
void resize( int **p, int size ) {
   free( *p );
   *p = (int*) malloc( size * sizeof(int) );
   int tocpy[]= {8};

   /* showing offset from the beginning of an array*/
   memcpy(*p + size-1, tocpy, 1);
}
int main() {
   int *p;
   p =  calloc(10, sizeof(int));
   for (int i = 0; i < 10; i++)
        printf("p[i] %d\n", p[i]);
   resize( &p, 20 );
   for (int i = 0; i < 20; i++)
        printf("p2[i] %d\n", p[i]);
}