Reading strings doesn't work

I have this little code and I really can't figure out why it always gives me SIGSEGVs.

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

int read_strs(char **a, int *len) {

  int i;
  scanf("%d", len);
  if(*len <= 0) return 1;
  a = (char **) malloc(sizeof(char*) * (*len));
  if(a == NULL) return 1;
  for( i = 0; i < *len; i++ ) 
  {
      a[i] = malloc(sizeof(char) * 1000);
      scanf("%s", a[i]);
  }

  return 0;

}


int main(void) {
  int i, n;
  char **array;

  read_strs(array, &n);
  for( i = 0; i < n; i++ ) 
    printf("%s\n", array[i]);
    return 0;
}

It seems it doesn't even alloc the memory.