apue学习笔记（第十四章 高级I/O）

 1 #include "apue.h"
 2 #include <errno.h>
 3 #include <fcntl.h>
 4 
 5 char    buf[500000];
 6 
 7 int
 8 main(void)
 9 {
10     int        ntowrite, nwrite;
11     char    *ptr;
12 
13     ntowrite = read(STDIN_FILENO, buf, sizeof(buf));
14     fprintf(stderr, "read %d bytes\n", ntowrite);
15 
16     set_fl(STDOUT_FILENO, O_NONBLOCK);    /* set nonblocking */
17 
18     ptr = buf;
19     while (ntowrite > 0) {
20         errno = 0;
21         nwrite = write(STDOUT_FILENO, ptr, ntowrite);
22         fprintf(stderr, "nwrite = %d, errno = %d\n", nwrite, errno);
23 
24         if (nwrite > 0) {
25             ptr += nwrite;
26             ntowrite -= nwrite;
27         }
28     }
29 
30     clr_fl(STDOUT_FILENO, O_NONBLOCK);    /* clear nonblocking */
31 
32     exit(0);
33 }

 1 #include "apue.h"
 2 #include <errno.h>
 3 #include <fcntl.h>
 4 #include <sys/wait.h>
 5 
 6 int
 7 main(int argc, char *argv[])
 8 {
 9     int                fd;
10     pid_t            pid;
11     char            buf[5];
12     struct stat        statbuf;
13 
14     if (argc != 2) {
15         fprintf(stderr, "usage: %s filename\n", argv[0]);
16         exit(1);
17     }
18     if ((fd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC, FILE_MODE)) < 0)
19         err_sys("open error");
20     if (write(fd, "abcdef", 6) != 6)
21         err_sys("write error");
22 
23     /* turn on set-group-ID and turn off group-execute */
24     if (fstat(fd, &statbuf) < 0)
25         err_sys("fstat error");
26     if (fchmod(fd, (statbuf.st_mode & ~S_IXGRP) | S_ISGID) < 0)
27         err_sys("fchmod error");
28 
29     TELL_WAIT();
30 
31     if ((pid = fork()) < 0) {
32         err_sys("fork error");
33     } else if (pid > 0) {    /* parent */
34         /* write lock entire file */
35         if (write_lock(fd, 0, SEEK_SET, 0) < 0)
36             err_sys("write_lock error");
37 
38         TELL_CHILD(pid);
39 
40         if (waitpid(pid, NULL, 0) < 0)
41             err_sys("waitpid error");
42     } else {                /* child */
43         WAIT_PARENT();        /* wait for parent to set lock */
44 
45         set_fl(fd, O_NONBLOCK);
46 
47         /* first let‘s see what error we get if region is locked */
48         if (read_lock(fd, 0, SEEK_SET, 0) != -1)    /* no wait */
49             err_sys("child: read_lock succeeded");
50         printf("read_lock of already-locked region returns %d\n",
51           errno);
52 
53         /* now try to read the mandatory locked file */
54         if (lseek(fd, 0, SEEK_SET) == -1)
55             err_sys("lseek error");
56         if (read(fd, buf, 2) < 0)
57             err_ret("read failed (mandatory locking works)");
58         else
59             printf("read OK (no mandatory locking), buf = %2.2s\n",
60               buf);
61     }
62     exit(0);
63 }

 1 #include "apue.h"
 2 
 3 ssize_t             /* Read "n" bytes from a descriptor  */
 4 readn(int fd, void *ptr, size_t n)
 5 {
 6     size_t        nleft;
 7     ssize_t        nread;
 8 
 9     nleft = n;
10     while (nleft > 0) {
11         if ((nread = read(fd, ptr, nleft)) < 0) {
12             if (nleft == n)
13                 return(-1); /* error, return -1 */
14             else
15                 break;      /* error, return amount read so far */
16         } else if (nread == 0) {
17             break;          /* EOF */
18         }
19         nleft -= nread;
20         ptr   += nread;
21     }
22     return(n - nleft);      /* return >= 0 */
23 }

 1 #include "apue.h"
 2 
 3 ssize_t             /* Write "n" bytes to a descriptor  */
 4 writen(int fd, const void *ptr, size_t n)
 5 {
 6     size_t        nleft;
 7     ssize_t        nwritten;
 8 
 9     nleft = n;
10     while (nleft > 0) {
11         if ((nwritten = write(fd, ptr, nleft)) < 0) {
12             if (nleft == n)
13                 return(-1); /* error, return -1 */
14             else
15                 break;      /* error, return amount written so far */
16         } else if (nwritten == 0) {
17             break;
18         }
19         nleft -= nwritten;
20         ptr   += nwritten;
21     }
22     return(n - nleft);      /* return >= 0 */
23 }