UNIX环境编程学习笔记（8）——文件I/O之校验当前登录用户对文件的访问权限

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
int
main(int argc, char *argv[])
{
if (argc != ) {
printf("usage: accessdemo <pathname>");
exit(-);
}
if (access(argv[], R_OK) < ) {
printf("access error for %s: %s\n", argv[], strerror(errno));
} else {
printf("read access OK\n");
}
if (open(argv[], O_RDONLY) < ) {
printf("open error for %s: %s\n", argv[], strerror(errno));
} else {
printf("open for reading OK\n");
}
exit();
}

lienhua34:demo$ gcc -o accessdemo accessdemo.c
lienhua34:demo$ ls -l accessdemo
-rwxrwxr-x lienhua34 lienhua34 9月 : accessdemo
lienhua34:demo$ ./accessdemo accessdemo
read access OK
open for reading OK
lienhua34:demo$ ls -l /etc/shadow
-rw-r----- root shadow 4月 : /etc/shadow
lienhua34:demo$ ./accessdemo /etc/shadow
access error for /etc/shadow: Permission denied
open error for /etc/shadow: Permission denied
lienhua34:demo$ su
# chown root accessdemo
# chmod u+s accessdemo
# ls -l accessdemo
-rwsrwxr-x root lienhua34 9月 : accessdemo
# exit
exit
lienhua34:demo$ ./accessdemo /etc/shadow
access error for /etc/shadow: Permission denied
open for reading OK