设置文件的文件访问权限为：rw-r--r--

描述：rw- (user权限) / r– (group权限) / r– (others权限)

r: 读权限 w: 写权限 x: 执行权限

要求：输入文件名，打印输出该文件初始权限，以及修改为rw-r--r--后的权限

知识点：设置文件的多个权限位，对这些权限位进行按位或操作即可。S_IRUSR | S_IWUSR

代码:

#include<stdio.h>

#include<stdlib.h>

#include<unistd.h>

#include<errno.h>

#include<sys/types.h>

#include<sys/stat.h>

int main(int argc,char *argv[])

{

struct stat buf;

int res;

if(argc!=2)

{

perror("参数不正确!正确格式:./main filename");

exit(1);

}

res=stat(argv[1],&buf);

if(res<0)

{

perror("stat error");

exit(1);

}

printf("初始文件 %s 的权限信息:\n",argv[1]);

//if(buf.st_mode&S_IRWXU) printf("user read write execute\n");

if(buf.st_mode&S_IRUSR) printf("user read \n");

if(buf.st_mode&S_IWUSR) printf("user write \n");

if(buf.st_mode&S_IXUSR) printf("user execute\n");

//if(buf.st_mode&S_IRWXG) printf("group read write execute\n");

if(buf.st_mode&S_IRGRP) printf("group read \n");

if(buf.st_mode&S_IWGRP) printf("group write\n");

if(buf.st_mode&S_IXGRP) printf("group execute\n");

//if(buf.st_mode&S_IRWXO) printf("other read write execute\n");

if(buf.st_mode&S_IROTH) printf("other read \n");

if(buf.st_mode&S_IWOTH) printf("other write\n");

if(buf.st_mode&S_IXOTH) printf("other execute\n");

chmod(argv[1],S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);

res=stat(argv[1],&buf);

if(res<0)

{

perror("stat error");

exit(1);

}

printf("更改后文件 %s 的权限信息:\n",argv[1]);

if(buf.st_mode&S_IRUSR) printf("user read \n");

if(buf.st_mode&S_IWUSR) printf("user write \n");

if(buf.st_mode&S_IXUSR) printf("user execute\n");

if(buf.st_mode&S_IRGRP) printf("group read \n");

if(buf.st_mode&S_IWGRP) printf("group write\n");

if(buf.st_mode&S_IXGRP) printf("group execute\n");

if(buf.st_mode&S_IROTH) printf("other read \n");

if(buf.st_mode&S_IWOTH) printf("other write\n");

if(buf.st_mode&S_IXOTH) printf("other execute\n");

}