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[英]I am trying to validate the user input. But if i entered an invalid character the program goes to an infinite loop
[英]getpwnam() crashes program when invalid user is entered
在getuserinfo()中,如果行struct passwd * theUser = getpwnam(username); 尝试使用不存在的用户名,程序将以-1错误关闭。 它永远不会到达函数的错误处理部分。 它不会返回main,我不确定为什么。
它应该返回NULL并打印出错误消息,并让程序的其余部分尝试运行。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <ctype.h>
#include <string.h>
#include <pwd.h>
#include <grp.h>
#include <errno.h>
//awk 'BEGIN { FS=":"; print "User\t\tUID\n--------------------"; } { print $1,"\t\t",$3;} END { print "--------------------\nAll Users and UIDs Printed!" }' /etc/passwd
#define SHELLSCRIPT "\
#/bin/bash \n\
awk 'BEGIN { FS=\":\"; print \"User\t\tUID\n--------------------\"; } { print $1,\"\t\t\",$3;} END { print \"--------------------\nAll Users and UIDs Printed!\" }' /etc/passwd \n\
"
struct passwd *getuserinfo(char *username)
{
//Set errno to 0 so we can use it
errno = 0;
//create a variable to store the user info in
struct passwd *theUser = getpwnam(username);
//error check getpwnam()
if(theUser == NULL)
{
printf("getpwnam() ERROR, errno = %d", errno);
return NULL;
}
return theUser;
}
struct group *getgroupinfo(long int groupid)
{
//Set errno to 0 so we can use it
errno = 0;
//create a variable to store the group info in
struct group *theGroup = getgrgid(groupid);
//error check getgrgid()
if(theGroup == NULL)
{
printf("getgrgid() ERROR, errno = %d", errno);
return NULL;
}
return theGroup;
}
void displayusers()
{
system(SHELLSCRIPT);
}
/*
*
* 4. A main function which will
* Call getuserinfo passing a hard-coded username, and using the return object, display the user id. (10 points)
* Call getgroupinfo passing the return object from getuserinfo, and using the return object, display the user’s group name. (10 points)
* Call displayusers. (10 points)
*
* My main function does those things but I don't pass objects since the function prototypes you gave us
* don't accept that input, they want ints and strings
*/
int main(int argc, char **argv)
{
//Take in the username we want to look up
char username[50];
printf("Enter username: ");
scanf("%s", username);
//look up the user and get their info
struct passwd *theUser = getuserinfo(username);
//use the user's gid and look up its info
struct group *theGroup = getgroupinfo(theUser->pw_gid);
printf("User: %s\nUser ID: %d\nGroup Name: %s\n\n\n", theUser->pw_name, theUser->pw_uid, theGroup->gr_name);
displayusers();
return 0;
}
struct passwd *getuserinfo(char *username)
{
//define errno so we can use it
errno = 0;
//create a variable to store the user info in
struct passwd *theUser = getpwnam(username);
//error check getpwnam()
if(errno != 0)
{
perror("ERROR: getpwnam() FAIL");
}
//check if we got user data/if the user existed
else if(theUser == NULL)
{
fprintf(stderr, "ERROR: User does not exist!\n");
return NULL;
}
return theUser;
}
需要使用使用stderr的fprintf来确保始终显示错误消息。 它在printf缓冲区中丢失了,keithmo建议使用fflush(NULL)解决了这一问题。
errno用于检查呼叫是否成功。 然后我们确保theUser!= NULL,因为即使缺少用户,调用也会成功。 如果为NULL,我们会向用户打印一条错误消息,以便他们知道。
我们现在还按照t0mm13b在主函数中调用getgroupinfo之前进行错误检查
//look up the user and get their info
struct passwd *theUser = getuserinfo(username);
//use the user's gid and look up its info
struct group *theGroup;
if(theUser != NULL)
{
//get the user's group id
theGroup = getgroupinfo(theUser->pw_gid);
//print the user and group info
printf("User: %s\nUser ID: %d\nGroup Name: %s\n\n\n", theUser->pw_name, theUser->pw_uid, theGroup->gr_name);
}
else
{
fprintf(stderr, "ERROR: No group info, missing user!\n");
}
displayusers();
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