UNIXシステムコール ファイルをコピーする

#include <sys/types.h> /* open, read, write */
#include <stdio.h>     /* perror */
#include <stdlib.h>    /* exit */
#include <sys/stat.h>  /* open */
#include <fcntl.h>     /* open */
#include <sys/uio.h>   /* read, write */
#include <unistd.h>    /* close, read, write */

#define INFILE "input.file"
#define OUTFILE "output.file"

enum {
  BUFSIZE = 4,
};

int main(void) {
  int ifd, ofd;
  ssize_t cc;
  char buf[BUFSIZE];

  if ((ifd = open(INFILE, O_RDONLY)) == -1) {
    perror("open input file");
    exit(1);
  }

  if ((ofd = open(OUTFILE, O_WRONLY|O_CREAT|O_TRUNC, 0666)) == -1) {
    perror("open output file");
    exit(1);
  }

  while ((cc = read(ifd, buf, sizeof(buf))) > 0) {
    if (write(ofd, buf, cc) == -1) {
      perror("write");
      exit(1);
    }
  }

  if (cc == -1) {
    perror("read");
    exit(1);
  }

  if (close(ofd) == -1) {
    perror("close output file");
    exit(1);
  }

  if (close(ifd) == -1) {
    perror("close input file");
    exit(1);
  }

  return 0;
}

$ cat input.file 
abcdef

$ od -tx1 input.file 
0000000 61 62 63 64 65 66 0a

GDBによるデバッグ

(gdb) b main
(gdb) r
21        if ((ifd = open(INFILE, O_RDONLY)) == -1) {
(gdb) n
26        if ((ofd = open(OUTFILE, O_WRONLY|O_CREAT|O_TRUNC, 0666)) == -1) {
(gdb) p ifd
$1 = 3
(gdb) n
31        while ((cc = read(ifd, buf, sizeof(buf))) > 0) {
(gdb) p ofd
$2 = 4
(gdb) n
32          if (write(ofd, buf, cc) == -1) {
(gdb) p buf
$3 = "abcd"
(gdb) p cc
$4 = 4
(gdb) n
31        while ((cc = read(ifd, buf, sizeof(buf))) > 0) {
(gdb) n
32          if (write(ofd, buf, cc) == -1) {
(gdb) p buf
$5 = "ef\nd"
(gdb) p cc
$6 = 3
(gdb) n
31        while ((cc = read(ifd, buf, sizeof(buf))) > 0) {
(gdb) n
38        if (cc == -1) {
(gdb) p buf
$7 = "ef\nd"
(gdb) p cc
$8 = 0