zerocount.c

zerocount.c

#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>

int main(int argc, char **argv) {
  if (argc < 2) {
    fprintf(stderr, "usage: %s FILE\n", argv[0]);
    return 1;
  }
  int fd = open(argv[1], O_RDONLY);
  if (fd < 0) {
    perror("open");
    return 1;
  }
  struct stat s;
  if (fstat(fd, &s) < 0) {
    perror("stat");
    return 1;
  }
  size_t size = s.st_size;
  const char *map = mmap(0, size, PROT_READ, MAP_PRIVATE, fd, 0);
  if (map == MAP_FAILED) {
    perror("mmap");
    return 1;
  }
  long long zero_cnt = 0, cnt = 0;
  for (size_t i = 0; i < size; ++i) {
    cnt++;
    if (!map[i]) {
      zero_cnt++;
    }
  }
  printf("total bytes: %lld, zero bytes: %lld\n", cnt, zero_cnt);
  return 0;
}