open_read.c

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
inline int get_fsize(int fd) {
  struct stat sb;
  int err;
  err = fstat(fd, &sb);
  if (err) {
    fprintf(stderr, "fstat error! [%s]\n", strerror(errno));
    return -1;
  }
  return sb.st_size;
}
 
int main(int argc, char *argv[]) {
 
  int fd;
  char *path;
  char buf[65536];
  int i, cnt = 0;
  int offset, chunk_size, fsize;
  int length;
 
  if (argc < 2) {
    fprintf(stderr, "require file path.\n");
    return -1;
  }
  path = argv[1];
 
  fd = open(path, O_RDONLY);
  fsize = get_fsize(fd);
  if (fsize < 0) {
    return -1;
  }
  
  offset = 0;
  while (offset != fsize) {
    chunk_size = fsize - offset;
    if (chunk_size > sizeof(buf))
      chunk_size = sizeof(buf);
    length = read(fd, buf, chunk_size);
    if (length != chunk_size) {
      fprintf(stderr, "read error! [%d]\n", length);
      break;
    }
    for (i=0; i<length; i++) {
      if (buf[i] == 0x00) cnt++;
    }
    offset += chunk_size;
  }
 
  close(fd);
 
  printf("%s: size=%d cnt=%d\n", path, fsize, cnt);
 
  return 0;
}