Get chunk size for a malloc allocation

malloc_chunk.c

/*
Get chunk size for a malloc allocation
*/

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

#define NO_FLAGS ~0x7

int main(int argc, char** argv) {

  if (argc < 2) {
    printf("Usage: %s <malloc-size>\n", argv[0]);
    return 1;
  }
  
  int malloc_size = atoi(argv[1]);
  void* chunk = malloc(malloc_size);

  // access to size member of chunk
  size_t chunk_size = *((size_t*)chunk - 1);

  printf("chunk size: 0x%lx\n", chunk_size & NO_FLAGS);

  return 0;
}