Problem I can't seem to solve

Hello all

I've got an assignment to make a quiz.
First of all one must be able to create users with a passwords
when the program starts, it ask if you want to create a user/pass or login


creating I've done... it writes all the users to a file
both username and password are max 15 long...
they are written to a binary file :

----15 for username----- 15 for pasword----- (without the trails.. it's just white spaces)


now when I want to test my login. i've got a problem:

I first ask the user to enter pass en login
I save this but the watch of my compiler tells me it just saved what I write and not the 15 long

so during the stringcompare it's logical it doesn't compare:

more info on the script:

let's imagine i enter user1 and pass1
and that inside the file it says user1 and pass1:

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <conio.h>


int login(void){

char user[15];
char pass[15];
char temp_user[17];
char temp_pass[17];
int sw_ok=1;
FILE *login;

clrscr();
printf("\t**********************************************\n");
printf("\t*                  Login                     *\n");
printf("\t**********************************************\n");

while (sw_ok)
{
login=fopen("users.dat", "rb");  
printf("username: ");
scanf("%15s", user); //according to watch it store "user1"
printf("Paswoord: ");
scanf("%15s", pass);  //according to watch it stores "pass1"


while(!feof(login))
{
	 fgets(temp_user,sizeof(user)+1,login); //gets "          user1"
	 fgets(temp_pass,sizeof(pass)+1,login); //gets "         pass1"
	

		if (strcmp(temp_user, user) == 0 && strcmp(temp_pass, pass) ==0) {
			printf("\nAccess OK\n");
			sw_ok=0;
			}
		else printf("\incorrect\n");

}



}
printf("Tataaaa");
return 0;
}

thanks for some feedback...

FAQ > How do I... (Level 1) > Get a line of text from the user/keyboard (C)
FAQ > Explanations of... > Why it's bad to use feof() to control a loop

Why binary mode for strings? If you really need binary mode, shouldn't you use fread instead of fgets?

Do you really need clrscr and conio.h?

[edit]

Code:

fgets(temp_user,sizeof(user)+1,login);

Read one less than the string can hold (even when accounting for the null character), but disguise it to look like it's reading one more than it should?

Kinda the same thing here:

Code:

scanf("%15s", user);

What's \i?

Code:

else printf("\incorrect\n");

Is login a FILE* or a function?

Code:

int login(void){

char user[15];
char pass[15];
char temp_user[17];
char temp_pass[17];
int sw_ok=1;
FILE *login;

Hey Dave,
He's probably using clrscr() so that when he calls this program from cmd.exe or any other command line app all of the garbage above will be removed so that the program will start out with a fresh screen, it all comes down to aesthetics.

Originally Posted by Kleid-0

Hey Dave,
He's probably using clrscr() so that when he calls this program from cmd.exe or any other command line app all of the garbage above will be removed so that the program will start out with a fresh screen, it all comes down to aesthetics.

I'm aware of what it does. I'm also aware of senior programmers who could detail why doing so is "unnecessary and anti-social".

What!? C'mon Dave, that's just silly.

http://cboard.cprogramming.com/search.php

Originally Posted by Dave_Sinkula

Why binary mode for strings? If you really need binary mode, shouldn't you use fread instead of fgets?

I use binary because a txt file would enable users to go look into the txt file. Ok one could say they just have to open the file in notepad to see it too.... but not everyone knows that. + I still need to find a way to "encrypt" the writing to a file.


thanks for the feedback, I'll change the loop with feof like the tutorial explains...

here are the answers to your questions:

Originally Posted by Dave_Sinkula

Do you really need clrscr and conio.h?

yes I do... before entering this function, the screen needs to be cleared because they already got an intro function with a header, menu ...
anyway this is just esthetics...

Originally Posted by Dave_Sinkula

[edit]

Code:

fgets(temp_user,sizeof(user)+1,login);

Read one less than the string can hold (even when accounting for the null character), but disguise it to look like it's reading one more than it should?

well this is odd I must admit... but without the +1 the watch tells me it reads in "[blank spaces]... user" (it omits the last character.. here a 1 )
by doing the +1 it reads the info correctly...: "[blankspaces]....user1"

Originally Posted by Dave_Sinkula

Kinda the same thing here:

Code:

scanf("%15s", user);

I put this because I made a limit that max. 15 characters are to be used for login and password...

+ I was hoping by putting this like that... when a user enters for instance user1

it would store it like this " user1"

thus the strcmp between this and the sequence read out of the file would be equal
and thus result in "login ok"

Originally Posted by Dave_Sinkula

What's \i?

Code:

else printf("\incorrect\n");

sorry typo after having paste it into this box

Originally Posted by Dave_Sinkula

Is login a FILE* or a function?

Code:

int login(void){

char user[15];
char pass[15];
char temp_user[17];
char temp_pass[17];
int sw_ok=1;
FILE *login;

good point...
I renamed the function to "inloggen" (dutch)

this function is called out from the main function..



thanks for the feedback...

Originally Posted by psykik

I put this because I made a limit that max. 15 characters are to be used for login and password...

And this doesn't account the null character.

Food for thought...

Code:

#include <stdio.h>
#include <string.h>

char *foo(char *line, int size, const char *prompt)
{
   fputs(prompt, stdout);
   fflush(stdout);
   if ( fgets(line, size, stdin) )
   {
      char *newline = strchr(line, '\n');
      if ( newline != NULL )
      {
         *newline = '\0';
      }
   }
   return line;
}

int main(void)
{
   char file_user[15] = "         user1";
   char file_pass[15] = "         pass1";
   char user [ sizeof file_user + 1/* expect trailing newline with fgets*/ ];
   char pass [ sizeof file_pass + 1/* expect trailing newline with fgets*/ ];
   static const char filename[] = "users.dat";
   FILE *file = fopen(filename, "wb");
   if ( file )
   {
      fwrite(file_user, sizeof file_user, 1, file);
      fwrite(file_pass, sizeof file_pass, 1, file);
      fclose(file);
   }
   foo(user, sizeof user, "username: ");
   foo(pass, sizeof pass, "password: ");
   file = fopen(filename, "rb");
   if ( file )
   {
      while ( fread(file_user, sizeof file_user, 1, file) == 1 &&
              fread(file_pass, sizeof file_pass, 1, file) == 1 )
      {
         if ( strcmp(file_user, user) == 0 && strcmp(file_pass, pass) == 0 )
         {
            puts("Access OK");
            goto done;
         }
      }
      puts("Invalid Access");
      done:
      fclose(file);
   }
   return 0;
}

/* my output
username: user1
password: pass1
Invalid Access

username:          user1
password:          pass1
Access OK
*/

thanks for the code and alternative way...

I've been looking into how to do it also
and came up with this:


(sorry if the code is lame... I'm still quite new at C)
also the printf's are in dutch...

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>


int inloggen(void){

char user[15];
char pass[15];
char **temp_user,**temp_pass,lijn[31],c='o'; //15+15+1
//int's voor de lussen...
int sw_ok=1, sw_user=1, sw_pass=1,sw_gevonden=0,lengte=0,i=0;
FILE *login;


printf("\t**********************************************\n");
printf("\t*                  Login                     *\n");
printf("\t**********************************************\n");

login=fopen("users.dat", "rb");
fscanf(login,"%*s");
	 while(!feof(login))
	 {	  lengte++;
		  fscanf(login,"%*s");
	 }
	 rewind(login);
	 temp_user=calloc(sizeof(char*),lengte);
	 temp_pass=calloc(sizeof(char*),lengte);
	 for(i=0;i<lengte;i++)
	 {   fscanf(login,"%s",lijn);
		  temp_user[i]=malloc(16);
		  strncpy(temp_user[i],lijn,15);
		  fscanf(login,"%s",lijn);
		  temp_pass[i]=malloc(16);
		  strncpy(temp_pass[i],lijn,15);
	 }
	 fclose(login);

while (sw_ok)
{
	while(sw_user)
	{
		printf("Gebruikersnaam: ");
		scanf("%15s%c", user,&c);
		if(c!='\n')
		{
			printf("Deze gebruikersnaam is te lang. U kan enkel een gebruikersnaam gebruiken van 15 karakters.\n");
			scanf("%*[^\n]%*c");
		}
		else sw_user=0;
	}

	while(sw_pass)
	{
		printf("Geef uw paswoord: ");
		scanf("%15s%c",pass,&c);
		if(c!='\n')
		{
			printf("Foutief paswoord...(te lang, max 15 karakters)\n");
			scanf("%*[^\n]%*c");
		}
		else sw_pass=0;
	}


for(i=0;i<lengte;i++){
	if (strcmp(temp_user[i], user) == 0 && strcmp(temp_pass[i], pass) ==0){
							sw_ok=0;
							sw_gevonden=1;
				}
				else  {
					sw_user=1;
					sw_pass=1;
					}
	 }//einde for lus
if (sw_gevonden)
{
printf("***********************\n");
printf("*     Toegang OK      *\n");
printf("***********************\n");
menu();
}
else printf("Foute gebruikersnaam of paswoord\nProbeer opnieuw AUB\n");
}
	return 0;
}

Dave!? First you say clrscr() is antisocial, and now you use goto. Are you going through tough times?

There's a difference: goto is standard.

Quzah.

Well I think goto is antisocial.

Goto is anything but antisocial. It's always going places.

Quzah.

omg I'm going insane, AAHH!!!

*bump*

I believe this works well without a goto:

Code:

#include <stdio.h>
#include <string.h>
#include <assert.h>

char *getLine( char *l, int size, const char *prompt )
{
	int i, c;

	printf( "%s ", prompt );
	for( i=0; i<size-1 && ( c=getc( stdin ) )!=EOF && c!='\n'; ++i )
		l[i]=c;
	l[i]='\0';
	
	return l;
}


int main( void )
{
	char file_user[] = "birds";
	char file_pass[] = "sing";
	char user [ sizeof( file_user ) + 1 ];
	char pass [ sizeof( file_pass ) + 1 ];
	static const char filename[] = "users.dat";
	FILE *file = fopen( filename, "w" );
	
	/* Write the correct username/password to the file */
	assert( file );
	if( file )
	{
		fwrite( file_user, sizeof( file_user ), 1, file );
		fwrite( file_pass, sizeof( file_pass ), 1, file );
		fclose( file );
		file = NULL;
	}
	
	/* Get a username/password from the user */
	getLine( user, sizeof( user ), "username: " );
	getLine( pass, sizeof( pass ), "password: " );
	
	/* Prepare to read the file */
	file = fopen( filename, "r" );
	assert( file );
	
	/* Get the correct username/pass from file */
	if( !feof( file ) && !ferror( file ) )
		fread( file_user, sizeof( file_user ), 1, file );
	if( !feof( file ) && !ferror( file ) )
		fread( file_pass, sizeof( file_pass ), 1, file );
		
	/* Make sure the username/pass are correct */
	if( !strcmp( file_user, user ) && !strcmp( file_pass, pass ) )
		puts( "Access OK" );
	else
		puts( "Invalid Access" );

	/* Close the stream */
	fclose( file );
	
	/* Return successful */
	return 0;
}