APUE-文件與目錄：一個LINUX用戶登陸函數

<pre name="code" class="cpp">#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pwd.h>
#include <shadow.h>
#include <string.h>
#include <termios.h>

pid_t sysuser_login(void);
int input_sw(int echo, int block);
int pass_shadow( char *passwd);
int user_shadow(char *user);

int main()
{
	pid_t pid;
	char ch;
	while(1)
	{
		pid = sysuser_login();
		if(pid == -2) 
		{
			printf("no such user in system!\n");
		}
		else if(pid == -1)
		{
			printf("\nyou password is error\n");
		}
		else printf("\n%d load in system success!\n", pid);
		printf("Do you want to continue?<y/n> ");
		if((ch = getchar()) == 'n') break;
		getchar();
	}

	return 0;
	
}

int input_sw(int echo, int block)
{
    struct termios set;
  	tcgetattr(STDIN_FILENO,&set);
    if(echo)    set.c_lflag |= ECHO;
  	else        set.c_lflag &=~ECHO;
    if(block)   set.c_lflag |= ICANON;
    else        set.c_lflag &=~ICANON;
    tcsetattr(STDIN_FILENO, TCSAFLUSH, &set);
}

int pass_shadow( char *passwd)
{
	int i = 0;
	char ch;
	input_sw(0,0);
	while((ch = getchar()) != '\n')
	{
		if(ch == 27)
		{
			if(i != 0)
			{
				i--;
				printf("\b \b");
			}
			continue;
		}
		putchar('*');
		passwd[i++] = ch;
	}
	passwd[i] = '\0';
	input_sw(1,1);
	return 0;
}

int user_shadow(char *user)
{
	int i = 0;
	char ch;
	input_sw(0,0);
	while((ch = getchar()) != '\n')
	{
		if(ch == 27)
		{
			if(i != 0)
			{
				i--;
				printf("\b \b");
			}
			continue;
		}
		putchar(ch);
		user[i++] = ch; 
	}
	user[i]= '\0';
	printf("\n");
	input_sw(1,1);
	return 0;
}

pid_t sysuser_login(void)
{
	struct spwd *spwd;
	struct passwd *pass;
	char user[32];
	char passwd[32];
	char *sha;
	char salt[32];
	printf("Please input username: ");
	user_shadow(user);
	spwd = getspnam(user);
	pass = getpwnam(user);
	if(NULL == pass || NULL == spwd) return -2;
    printf("Please input password: ");
    pass_shadow(passwd);
	int i = 0;
	int flag = 0;
	while(flag < 3)
	{
		if(spwd->sp_pwdp[i] == '$')  flag++;
		salt[i] = spwd->sp_pwdp[i];
		i++;
	}
	salt[i] = '\0';
	sha = crypt(passwd, salt);
	if(strcmp(sha, spwd->sp_pwdp) == 0) return (pass->pw_uid);
	else return -1;
}