Linux C 程序 (15)

dup ,dup2,fcntl,ioctl系统调用

1 1. dup ,dup2 函数
2 int dup(int oldfd)
3 int dup(int oldfd , int newfd)

dup用来复制参数oldfd的文件描述符
duo2可以用newfd来指定新文件描述符的数值

2.fcntl函数
对已经打开的文件描述符进行各种控制操作，以及改变已经打开文件的各种属性

3.ioctl函数
控制设备，不能用其他函数进行控制操作都可以用ioctl来进行

3.文件属性的操作
 1.  shell里可通过ls来获取文件属性，那么在程序里怎么获取文件属性呢？
         用到stat/fstat/lstat

1         man 2 stat
2          #include<sys/types.h>
3          #include<sys/stat.h>
4          #include<unistd.h>
5          int stat(const char *file_name,struct stat *buf);
6          int fstat(int filedes,struct stat *buf);
7          int lstat(const char *fime_name ,struct stat *buf);

stat 获取由参数file_name指定的文件名的状态信息，保存参数到struct stat *buf中
         fstat   与stat 区别，fstat通过文件描述符来指定文件
         lstat  与stat，对于符号连接文件，lstat返回的是符号连接文件本身的状态信息。而stat返回的是符号连接文件指向的文件的状态信息。

 1            struct stat {
 2                dev_t     st_dev;     /* ID of device containing file */
 3                ino_t     st_ino;     /* inode number */
 4                mode_t    st_mode;    /* protection */
 5                nlink_t   st_nlink;   /* number of hard links */
 6                uid_t     st_uid;     /* user ID of owner */
 7                gid_t     st_gid;     /* group ID of owner */
 8                dev_t     st_rdev;    /* device ID (if special file) */
 9                off_t     st_size;    /* total size, in bytes */
10                blksize_t st_blksize; /* blocksize for file system I/O */
11                blkcnt_t  st_blocks;  /* number of 512B blocks allocated */
12                time_t    st_atime;   /* time of last access */
13                time_t    st_mtime;   /* time of last modification */
14                time_t    st_ctime;   /* time of last status change */
15            };

eg:获取文件属性
                                                                                                                                                                                              79,0-1        Bot

 1 #include<stdio.h>
 2 #include<time.h>
 3 #include<sys/stat.h>
 4 #include<unistd.h>
 5 #include<sys/types.h>
 6 #include<errno.h>
 7
 8 int main(int argc , char * argv[]){
 9         struct stat buf;
10         /*check param number*/
11         if(argc != 2){
12                 printf("Usage mystat  <file_name>\n");
13                 exit(0);
14         }
15         /*get file attr*/
16         if(stat(argv[1],&buf) == -1){
17                 perror("stat:");
18                 exit(1);
19         }
20         //print file attr
21         printf("device is :%d\n",buf.st_dev);
22         printf("inode is :%d\n",buf.st_ino);
23         printf("mode is :%d\n",buf.st_mode);
24         printf("number of hard links  is :%d\n",buf.st_nlink);
25         printf("user ID of owner  is :%d\n",buf.st_uid);
26         printf("group ID of owner  is :%d\n",buf.st_gid);
27         printf("device type (if inode device ) is :%d\n",buf.st_rdev);
28
29         printf("total size ,in bytes  is :%d\n",buf.st_size);
30         printf("blocksize for filesystem I/O  is :%d\n",buf.st_blksize);
31         printf("number of blocks allocated is :%d\n",buf.st_blocks);
32
33         printf("time of last access  is :%s\n",ctime(&buf.st_atime));
34         printf("time of last modification  is :%s\n",ctime(&buf.st_mtime));
35         printf("time of last change  is :%s\n",ctime(&buf.st_ctime));
36
37         return 0;
38
39 }
40 output ：
41 [[email protected] C]$ ./my_chmod  example.c
42 device is :2050
43 inode is :407124
44 mode is :33152
45 number of hard links  is :1
46 user ID of owner  is :500
47 group ID of owner  is :500
48 device type (if inode device ) is :0
49 total size ,in bytes  is :0
50 blocksize for filesystem I/O  is :4096
51 number of blocks allocated is :0
52 time of last access  is :Mon Jan  5 23:23:36 2015
53 time of last modification  is :Mon Jan  5 23:29:37 2015
54 time of last change  is :Mon Jan  5 23:29:37 2015

2.设置文件属性

 1 chmod/fchmod , chown/fchown/lchown,truncate/ftruncate,utime,umask
 2 1.chmod/fchmod
 3 修改文件的存取权限
 4 2.chown/fchown/lchown
 5 修改文件的用户id和组id
 6 3.ftruncate/truncate
 7 改变文件大小
 8 4.utime
 9 改变文件的st_mtime和st_ctime域，即存取时间和修改时间。
10 5.umask
11 使用文件创建时使用的屏蔽字