mmap character reading example

mmap example

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

//takes a filename as 1st argument
//opens it, and mmaps the whole thing.
//demonstrates the use of mmap for character 
//reading
int main(int argc, char **argv) {

  int i, fd, pagesize;
  char *data;
  struct stat file_status;
  unsigned long int bytes_read, bytes_left, to_read;

  fd = open(argv[1], O_RDONLY);
  fstat(fd, &file_status);

  pagesize = getpagesize();
  bytes_left = file_status.st_size;
  while(bytes_left > 0) {

    if(bytes_left > pagesize) {
      to_read = pagesize;
    } else {
      to_read = bytes_left;
    }

    data = mmap((caddr_t)0, to_read, PROT_READ, MAP_SHARED, fd, bytes_read);
    for(i = 0; i < to_read; i++) {
      /*putchar(data[i]);*/
    }
    munmap(data, to_read);

    bytes_read += to_read;
    bytes_left -= to_read;

  }

  return EXIT_SUCCESS;
}