comparison pointer and integer

**plodos** · 01-09-2009

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <ctype.h>
#include <time.h>
#include <sys/types.h>

char *password;
char *username;
char *path;
char  usernameLogin;
char  passwordLogin;

int main ( void )
{
static const char filename[] = "ogr.txt";
FILE *file = fopen ( filename, "r" );
int i, j;
char arra[128][128];
char line[128];


    for(i=0; i<128; i++)
        for(j=0; j<128; j++)
        arra[i][j] = '\0';

    for(i=0; i<128; i++)
    line[i] = '\0';

    if ( file != NULL )
    {
       i=0;

        while ( fgets ( line, sizeof line, file ) != NULL )
        {
            strcpy(arra[i], line);
            i++;
             username = arra[0];
             password = arra[1];
             path     = arra[2];
        }
      //  printf("username=%s password=%s path=%s ", username,password,path);
         printf("type username :"); scanf("%s",&usernameLogin); printf("\n");
         printf("type password :"); scanf("%s",&passwordLogin); printf("\n");


         if(usernameLogin==username &&  passwordLogin==password)
         {
           printf("Correct!");
         }
         else
         {
           printf("Wrong!");
         }       
     fclose ( file );
    }
    else
    {
        perror ( filename );
    }
return 0;
}

ogr.txt

Code:

20009874 //uname
9874        /pword
desktop //path

these are pointers which is getting the values from file
username = arra[0];
password = arra[1];
path = arra[2];

but usernameLogin and passwordLogin are not pointer
if(usernameLogin==username && passwordLogin==password)
{
printf("Correct!");
}
else
{
printf("Wrong!");
}

how can I compare the pointer and normal variable ?
I want to make read from file and login!

**Elysia** · 01-09-2009

1) char is not a string. You cannot store a string in a char. A char contains a character, such as 's'. A string is an array of chars.
2) I urgue you to read http://apps.sourceforge.net/mediawik...tle=Scanf_woes
3) Realize that you are not copying the actual password or username with your assignment. You are assigning an address, so whenever you read new data from the file, username and password will lose its previous values.
4) Use strcmp to compare strings.

**laserlight** · 01-09-2009

Originally Posted by plodos

but usernameLogin and passwordLogin are not pointer

They should be arrays of char instead.

The way I see it, you are overcomplicating things with your arra and line variables. You just need password, username, path, usernameLogin and passwordLogin to be arrays of char. They should also be local variables instead.

**matsp** · 01-09-2009

But usernameLogin and passwordLogin are only one char each - and when compared to the pointer to char, that gets converted to an integer [char really is a integer of tiny size], so you ARE comparing usernameLogin (an integer) with username (a pointer).

Even if both of them where pointers, you can not compare strings this way in C - you need to use strcmp().

Why are you using global variables? [further, those global variables point to local variables - that is indeed a VERY good way to get very strange results if you ever do this in any function other than main - as the space used by local variables is freed when the function leaves, and later on will get used for other purposes].

**plodos** · 01-09-2009

thnx for urgent reply but the another problem is
i dont know how to apply

is it possible go get values from the file without using pointers?
than I can compare only the strings ( i will change char to string for all of them )

if its possible can u write the sample code for me :s

**Elysia** · 01-09-2009

You need to take a step back and learn C properly, or alternatively, switch to another language, before proceeding.
Learn how to use strings, first of all.

**matsp** · 01-09-2009

Originally Posted by plodos

if its possible can u write the sample code for me :s

No, we do not do homework for you - see the
http://cboard.cprogramming.com/annou...t.php?f=4&a=39

--
Mats

**Elysia** · 01-09-2009

Helpful links:
http://www.cprogramming.com/tutorial/c/lesson9.html
http://www.cprogramming.com/tutorial/c/lesson6.html

**plodos** · 01-09-2009

Code:

char  usernameLogin[10];
char  passwordLogin[10];
char *usernameLoginP;
char *passwordLoginP;

//same code

         printf("type username :"); scanf("%s",&usernameLogin); printf("\n");
         printf("type password :"); scanf("%s",&passwordLogin); printf("\n");
         
         usernameLoginP = &usernameLogin;
         passwordLoginP = &passwordLogin;

         // pointer to pointer
         if(*usernameLoginP==username &&  passwordLogin==password)

cannot convert `char (*)[10]' to `char*' in assignment ... Why ?

**Elysia** · 01-09-2009

Because arrays decay to a pointer to the first element. You are trying to assign a pointer to an array, which is different.

usernameLoginP = usernameLogin;
passwordLoginP = passwordLogin;

This will work.
You must still read http://apps.sourceforge.net/mediawik...tle=Scanf_woes

**plodos** · 01-09-2009

thank you

but :s

Code:

 usernameLoginP = usernameLogin;
         passwordLoginP = passwordLogin;

         printf("usernameLoginP=%s\n",usernameLoginP); // usernameLoginP=20009874
         printf("username=%s\n",username);                      // usernameLogin=20009874
         if(usernameLoginP==username )
         {
           printf("Correct!");
         }
         else
         {
           printf("Wrong!");
         }

it return wrong! but the values are correct, WHY the comparision is not working ?

**matsp** · 01-09-2009

Originally Posted by plodos

thank you

but :s

Code:

 usernameLoginP = usernameLogin;
         passwordLoginP = passwordLogin;

         printf("usernameLoginP=%s\n",usernameLoginP); // usernameLoginP=20009874
         printf("username=%s\n",username);                      // usernameLogin=20009874
         if(usernameLoginP==username )
         {
           printf("Correct!");
         }
         else
         {
           printf("Wrong!");
         }

it return wrong! but the values are correct, WHY the comparision is not working ?

Because you are still not using strcmp(). You are checking if userNameLoginP has the same address as username - which obviously would not be the case, as they are distinct different arrays.

--
Mats

**Elysia** · 01-09-2009

When comparing arrays, the array turns into a pointer to the first element and when comparing to a pointer, well, you are comparing its contents - an address!
So unless the both sides have the same contents (ie point to the same place, same value)...
Well, you get what I'm getting at, right?

**plodos** · 01-09-2009

but the outputs are same and decimal

Code:

printf("usernameLoginP=%s\n",usernameLoginP); // usernameLoginP=20009874
         printf("username=%s\n",username);                      // usernameLogin=20009874

strcmp();

Code:

if( strcmp(username, usernameLoginP  ) == 0 )
         {
           printf("Correct!");
         }

I lost myself

**Elysia** · 01-09-2009

But basically you are comparing two pointers. Pointers store a memory address. In your case, those pointers would point to the same value, but at two different locations in memory.
And as pointers are variables, the contents of those variables are compared (and pointers contains memory addresses!), so since the contents of the pointers is not the same, the comparison is false!
That is why there is such a function as strcmp.
C was made to be efficient, not programmer friendly.

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