comparison pointer and integer

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!

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.

Quote:

---

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.

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].

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

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.

Quote:

---

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

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

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 ?

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

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 ?

Quote:

---

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

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?

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

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.

Elysia you know what are you doing but im not :)

If you did similar things, just give me an idea or hint! ( ex: can I do it without using pointers )

in my humble opinion, pointer is not for me

Thanks in advance

Arrays can act like pointers, but if you do it right, there will not be a problem. You must learn pointers sooner or later (or you can forget C altogether).
To compare two strings (be they stored in pointer or arrays doesn't matter), use strcmp. As simple as that.

When you print using printf() and %s format, you are not printing the address of the string, are you? If you do

Code:

---

printf("username = %p, usernameLoginP=%p", username, usernameLoginP);

---

Do you still get the same value? Probably not. That is what "usernam == usernameLoginP" is comparing - and if they aren't the same in the printout, then they are also not the same in the comparison.

strcmp() does something along the lines of:

Code:

---

int strcmp(char *s1, char *s2)
{
    while(*s1 && *s1 == *s2)  // Exit when we hit a "zero", or when the characters are different. 
    {
      s1++;
      s2++;
    }
    return *s2 - *s1;  // If they are different, return a signed indication of which is greater.
}

---

This walks through the two arrays (or blocks of memory) until it finds either the end of the first string, or the strings are different (which also happens if the second string is shorter than the first string). That is different from comparing s1 with s2 - that's the location of the string.

--
Mats

hımm I understood it now.

Code:

---

printf("usernameLoginP=%p\n",usernameLoginP);  //0040,,,,
        printf("username=%p\n",username);  //0022cc...
        if( strcmp(username, usernameLoginP  ) == 0 )  // comparing the addresses
        {
          printf("Correct!");
        }

---

is it possible to convert username and usernameLoginP pointer to string :)
I dont know to escape from pointer

Quote:

---

Originally Posted by plodos

hımm I understood it now.

Code:

---

printf("usernameLoginP=%p\n",usernameLoginP);  //0040,,,,
        printf("username=%p\n",username);  //0022cc...
        if( strcmp(username, usernameLoginP  ) == 0 )  // comparing the addresses
        {
          printf("Correct!");
        }

---

is it possible to convert username and usernameLoginP pointer to string :)
I dont know to escape from pointer

---

A string in C is "a block of characters that end with a zero-value" - so a string is a pointer or array - and since arrays and pointers appear to be very similar in most aspects, you can most of the time use them interchangably [but beware that they ARE NOT THE SAME THING - just that they appear to be most of the time].

You comment "// comparing the addresses" is incorrect - strcmp() is comparing the CONTENT of the two strings passed in (as the address of the first character).

--
Mats