Show free memory on OS X

free.c

/*
 *  free.c - show free memory on OS X
 *  The api query code was extraced from Apple's vm_stat.c
 *  To compile: gcc -o free free.c
 *  Output: <byte count> <human readable bytecount>
 */

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

#include <mach/mach.h>


int humanize_byte_count(char (*r)[1024], double v) {
  int i = 0;
  char *units = "b KBMBGBTB";
  int max_unit = strlen(units) / 2;
  while (v > 1024 && i < max_unit) {
    v = v / 1024.0;
    i++;
  }
  snprintf((char *)r, 1023, "%0.2f%c%c", v, units[i*2], units[i*2+1]);
  return 1;
}

int main(int argc, char *argv[]) {
  vm_statistics64_data_t  vm_stat;
  mach_port_t host;
  char  *progname = argv[0];
  vm_size_t pageSize = 4096; 
  host = mach_host_self();
  if(host_page_size(mach_host_self(), &pageSize) != KERN_SUCCESS) {
    fprintf(stderr, "%s: failed to get pagesize; defaulting to 4K.\n",
        progname);
    pageSize = 4096;
  } 
  unsigned int count = HOST_VM_INFO64_COUNT;
  kern_return_t ret;
  if ((ret = host_statistics64(host, HOST_VM_INFO64, (host_info64_t)&vm_stat, 
      &count) != KERN_SUCCESS)) {
    fprintf(stderr, "%s: failed to get statistics. error %d\n", progname, ret);
    exit(EXIT_FAILURE);
  }
  uint64_t fm = vm_stat.free_count * pageSize;
  char hc[1024];
  humanize_byte_count(&hc, fm);
  printf("%lld %s\n", fm, hc);
  exit(EXIT_SUCCESS);
}