我目前正在编写的部分程序需要检查用户是否存在(这是针对 unix 系统的)。但是,在为用户读取密码文件时,永远不会到达 EOF,因此会形成无限循环。我可能做错了什么?
int readPass;
int userExists = 0; // 0 means user doesn't exist, 1 means they do
// open password file to read in usernames
int passFD = open("/etc/passwd", O_RDONLY);
// open password file to read character by character
FILE* pass = fopen("/etc/passwd", "r");
// c-string to store usernames
char passUser[100];
// read through the password file
while (readPass != EOF)
{
int numPass = 0;
// read until reaching a colon, this is the username of the current line
while (readPass != ':')
{
readPass = fgetc(pass);
numPass += 1;
}
// store username is a c-string
read(passFD, passUser, numPass);
passUser[numPass - 1] = '\0';
// if the user exists, stop checking
if ((strcmp(passUser, argv[user])) == 0)
{
userExists = 1;
break;
}
// read junk until next line
readPass = NULL;
int junksRead = 0;
char passJunk[100];
while (junksRead < 6)
{
numPass = 0;
readPass = NULL;
while (readPass != ':' && readPass != '\n' && readPass != EOF)
{
readPass = fgetc(pass);
numPass += 1;
//printf("%c\n", readPass);
}
read(passFD, passJunk, numPass);
junksRead += 1;
}
}
// if the user doesn't exist, end the program
if (userExists == 0)
{
printf("%s does not exist\n", argv[user]);
return 0;
}`
最佳答案
如果您没有其他选择,您可以通过自己阅读 /etc/passwd
文件来搜索用户。但是,更好的方法是使用可以为您执行此操作的现有函数:getpwnam()来自标题 pwd.h .无需重新发明已经完成和有效的东西。
可能的代码如下所示:
#include <stdio.h>
#include <pwd.h>
#include <errno.h>
int main()
{
//reset errno to be able to detect errors
errno = 0;
struct passwd * result = getpwnam("username");
//Return value NULL could either mean error or "user not found".
if (result == NULL)
{
//If errno is not zero, then an error occurred while getpwnam() was called.
if (errno != 0)
printf("An error occurred while searching for the user.\n");
//Otherwise the user just does not exist.
else
printf("User does not exist!\n");
}
//Not NULL: user was found.
else
{
printf("User exists.\n");
}
return 0;
}
关于c - 读取密码文件时,程序从未遇到 EOF,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/40642390/