CS471/571 - Operating Systems

Displaying exercises/e1/solution/to.c

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

#define K	1024

/**
 * This program should open a file (file-name given on the command line,) and
 * write to it all the data that is read from the standard input.  You may only
 * use the kernel system calls for I/O, you may not use any C standard library
 * I/O calls.  The file opened should be created if it does not exist and
 * truncated if it does.  An error should be displayed if the file cannot be
 * opened and the program should return an non-successful return value.
 * 
 * This program should do I/O in blocks of at least 1K at a time, it is not
 * correct to read and write only 1 byte at a time.
 */

int main(int argc, char *argv[])
{
  if (argc < 2) {
    printf("Usage: to <filename>\n");
    return 1;
  }
 
  int r, fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0666);
  char buf[K];
  
  if (fd < 0) {
    perror("File open");
    return 1;
  }
  
  while( (r = read(STDIN_FILENO, buf, K)) > 0) {
    write(fd, buf, r);
  }
  
  close(fd);
  return 0;
}