p4-5.c

UNIX程序设计教程

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "err_exit.h"
int main(void)
{
    const char  *path = "testfile";
    struct stat orig_buf, new_buf;
    int ngroups = getgroups(0, NULL);       /* 获取附加组个数（§5.8.4）*/
    /* 分配存放附加组ID的数组空间 */
    gid_t *groups = (gid_t *) malloc(ngroups * sizeof(gid_t));
    int val = getgroups(ngroups, groups);    /* 获取附加组ID于数组groups */
    printf("create testfile\n");
    creat(path, S_IRWXU | S_IRWXG | S_IRWXO);
    /* 查看这个新创建文件的用户ID、组ID和进程的附加组ID */
    stat(path, &orig_buf);
    printf("original owner-id=%d, group-id=%d,",
            orig_buf.st_uid, orig_buf.st_gid);
    if (val>1)
       printf(" supplementary group = %d\n",groups[1]);
    /* 改变文件的用户ID和组ID 至其它用户 */
    printf("set owner-id and group-id to 2 which is bin\n");
    if (chown(path, 2, 2) == 0) {
       printf("chown() call successful\n");
       stat(path, &new_buf);
       printf("new owner-id=%d, group-id=%d\n",
                  new_buf.st_uid, new_buf.st_gid );
    }
    else 
       perror("chown() call failed");
    /* 改变文件的用户ID和组ID 至附加组 */
    printf("set group-id to supplementary group\n"); 
    if (chown(path, orig_buf.st_uid, groups[1]) == 0 ) {
       printf("chown() call successful\n");
       stat (path, &new_buf);
       printf("new owner-id=%d, group-id=%d\n",
                  new_buf.st_uid, new_buf.st_gid );
    }
    else 
       perror("chown() call failed");
    fprintf(stdout,"remove testfile\n");
    remove(path);
}