Thread: Help in checking password in a file

Hi,

I need some serious help here.

How do i check a person userid and password and compare it with a file.

The file passwd.txt is as follows :

tan!susan 0321 john1
lee!jenny 0322 mary2
wong!chris 0333 chris3

I've managed to read the file using C.

Code:

#include<stdio.h>

main( )
 {
     FILE *fpassword;
     char c;
     int pass;
     fpassword = fopen("C:\PASSWD.TXT", "r");
     if (fpassword == NULL) printf("File doesn't exist\n");
     else
     {
         do {
                c = fgetc(fpassword);
                putchar(c);
            } while (c != EOF);

     }
    fclose(fpassword);

    getchar();
 }

But now how do i make check it's user id and password?

Meaning if the person enters :

Userid : john1
Password : 0321

It shows that the User is Authorized...?

How???

I'm not sure what is the username and what is the password in that file, but the general idea is to let the user input username/password, then the program will proceed to read each username/password combination from the file and compare those to the input. If no match is found, then the program fails.

Input can be done with cout to display something on the screen and cin to get data from the user. Although one might cosider using another function such as cin.get since cin by itself is not safe.
Store those in char arrays like

Code:

char username[100];

, then read from the file using some read techniques, which might be done in different amount of ways. One might be to read a line, then look for spaces and copy all that data into separate buffers for username, password and whatever more there is. Then you can compare the inputted username and password with strstr, which returns 1 if both strings you compare are equal.

Originally Posted by Elysia

I'm not sure what is the username and what is the password in that file, but the general idea is to let the user input username/password, then the program will proceed to read each username/password combination from the file and compare those to the input. If no match is found, then the program fails.

Input can be done with cout to display something on the screen and cin to get data from the user. Although one might cosider using another function such as cin.get since cin by itself is not safe.
Store those in char arrays like

Code:

char username[100];

, then read from the file using some read techniques, which might be done in different amount of ways. One might be to read a line, then look for spaces and copy all that data into separate buffers for username, password and whatever more there is. Then you can compare the inputted username and password with strstr, which returns 1 if both strings you compare are equal.

yeah, i need to compare the inputted username and password.

But i need to use C programming and not C++...

So how do i copy the data i read into separate buffers??? that's the thing i've really want to know???

Originally Posted by hk_mp5kpdw

This is the C board, not the C++ board.

cin and cout exists in standard C, as well, though there might be other functions to do such things.

Originally Posted by frodonet

yeah, i need to compare the inputted username and password.

But i need to use C programming and not C++...

So how do i copy the data i read into separate buffers??? that's the thing i've really want to know???

strcpy perhaps. Copies a string from one buffer to another. Otherwise you can use memcpy to copy memory from one buffer to another.

is the read function i use fgetc is not proper issit?

cause its reading by character?

so if i want to read by line i must use fgets?

You can do that too, but it's slower than reading a whole line at a time.

Originally Posted by hk_mp5kpdw

Read the users userid and password into two variables (character arrays).

How do i do this part??? sorry, but i'm seriously dumb with c.

Originally Posted by hk_mp5kpdw

Search through the file line-by-line (not character-by-character) and find a match with the userid and then check to see if the password field matches. Reading through the file can be a call to fgets to get individual lines combined with sscanf to parse out the individual fields in the line returned by the fgets call all in a while loop.
.

Is there any example i can refer for this part?

Originally Posted by Elysia

You can do that too, but it's slower than reading a whole line at a time.

i did try fgets...but i keep getting an error saying that "there are too few arguments".

if i want to use fgets, i must declare 2 variables for userid and password right?

and then, when i read using fgets....how should i continue with the sscanf...

Originally Posted by hk_mp5kpdw

Code:

char user[20];
printf("Enter userid: ");
fgets(user,sizeof(user),stdin);

Do something similar for the password.

hey thanks for your guidance...

just that i want to understand some things...

should i read the file first or should i prompt the user for userid and password first?

Originally Posted by frodonet

hey thanks for your guidance...

just that i want to understand some things...

should i read the file first or should i prompt the user for userid and password first?

It's really completely and absolutely up to you.

Personally, I'd read it after prompting. That way I can compare the password to the read password as it reads instead of storing the whole list in memory.

Originally Posted by MacGyver

lol....

I don't know much about all those CLI-like functions I only do Windows programming in C++.

Originally Posted by IceDane

It's really completely and absolutely up to you.

Personally, I'd read it after prompting. That way I can compare the password to the read password as it reads instead of storing the whole list in memory.

hi, this is my new code...i just managed to redo again.

Code:

#include<stdio.h>

main( )
 {
     FILE *fpassword;
     char c, line_buffer[100], user[20];
     int pass;
     fpassword = fopen("C:\\PASSWD.TXT", "r");
     if (fpassword == NULL) printf("File doesn't exist\n");

     printf("Enter userid: ");
     fgets(user,sizeof(user),stdin);

     printf("Enter password: ");
     fgets(pass,sizeof(pass),stdin);

     while( fgets(line_buffer,sizeof(line_buffer),fpassword) != NULL )  /* read from file while still data available */
     {
            char ftemp[20], fpass[20], fuser[20];
            if( sscanf(line_buffer,"%.20s %.20s %.20s",ftemp,fpass,fuser) != 3 )  /* Make sure we parsed 3 fields from the line */
            {
                 /* Invalid line in file, skip to next one   */
            }
            else /* Otherwise, we got 3 fields */
            {
                  if (user == fuser && pass = fpassword)
                  printf("User Authorized");
                  else
                  printf("User Not Authorized");
                  exit(0);
            }
}
    fclose(fpassword);

    getchar();
 }

there's this error saying that there's invalid lvalue in my assignment.

i think the part of my assignment of user==fuser is wrong? is it wrong?