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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 stat2 #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 attr21 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 [fubin@localhost C]$ ./my_chmod example.c42 device is :205043 inode is :40712444 mode is :3315245 number of hard links is :146 user ID of owner is :50047 group ID of owner is :50048 device type (if inode device ) is :049 total size ,in bytes is :050 blocksize for filesystem I/O is :409651 number of blocks allocated is :052 time of last access is :Mon Jan 5 23:23:36 201553 time of last modification is :Mon Jan 5 23:29:37 201554 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.umask11 使用文件创建时使用的屏蔽字
Linux C 程序 (15)
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