getpwnam函数学习

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getpwnam

　　 getpwnam()　　函数功能：获取用户登录相关信息　　

　　 原型定义: struct passwd *getpwnam(const char *name);

　　 表头文件:

　　#include <pwd.h>

　　#include <sys/types.h>

　　信息存贮在如下的结构体之中

　　struct passwd {

　　char * pw_name; /* Username. */

　　char * pw_passwd; /* Password. */

　　__uid_t -pw_uid; /* User ID. */

　　__gid_t -pw_gid; /* Group ID. */

　　char * pw_gecos; /* Real name. */

　　char * pw_dir; /* Home directory. -*/

　　char * pw_shell; /* Shell program. */

　　};

　　 例子：

#include <stdio.h>
#include <pwd.h>

int main()
{
        struct passwd * pw;
        char *username = "devis";
        pw = getpwnam(username);
        if(!pw)
        {
                printf("%s is not exist\n", username);
                return -1;
        }

        printf("pw->pw_name = %s\n", pw->pw_name);
        printf("pw->pw_passwd = %s\n", pw->pw_passwd);
        printf("pw->pw_uid = %d\n", pw->pw_uid);
        printf("pw->pw_gid = %d\n", pw->pw_gid);
        printf("pw->pw_gecos = %s\n", pw->pw_gecos);
        printf("pw->pw_dir = %s\n", pw->pw_dir);
        printf("pw->pw_shell = %s\n", pw->pw_shell);

        return 0;
}

 

运行的结果：

pw->pw_name = devis
pw->pw_passwd = x
pw->pw_uid = 500
pw->pw_gid = 500
pw->pw_gecos = devis
pw->pw_dir = /home/devis
pw->pw_shell = /bin/bash

 

下面是不可重入函数getpwnam的问题

 

#include <stdio.h>
 
#include <stdlib.h>
 
#include <unistd.h>
 
#include <signal.h>
 
#include <pwd.h>
 

void sig_handler(int signo);
 

int main(int argc, char** argv)
 
{
 
        int                             ret;
 
        
 
        struct passwd*                  ptr;
 
        signal(SIGALRM, sig_handler);
 
        alarm(1);
 
        for(; ;){
 
                ptr = getpwnam("xxxx");
 
                if(ptr == NULL){
 
                        perror("getpwnam");
 
                        exit(1);
 
                }
 
                if(strcmp(ptr->pw_name, "xxxx") != 0){
 
                        printf("return value has corrupted by sig_handler, pw_name = %s\n", ptr->pw_name);
 
                }
 
        }
 

        exit(0);
 
}
 

void sig_handler(int signo)
 
{
 
        struct passwd*                  root_ptr;
 

        printf("in sig_handler\n");
 
        root_ptr = getpwnam("root");
 
        if(root_ptr == NULL){
 
                perror("sig_usr getpwnam");
 
                exit(2);
 
        }
 
        printf("pw_name = %s\n", root_ptr->pw_name);
 
        alarm(1);
 
}

 

getpwnam是不可重入函数。因此此程序运行的结果是不可预见的。

 

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