Thread: Looping with strcat

Hello

I'm having a problem with my program. What it does is take the input in 1 character at a time, replace it with a '*', and when enter is pressed, check to see if it is the correct password.

I have diagnosed the problem being with the strcat function. When it's commented out, the other code works fine. The program stops working after 2 characters are inputed. Thanks for your help!

Code:

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

int main()
{
    char password[] = "cheese";
    char input_pass[10] = "";
    char c;
    
    int t = 0;
    int r;
    
    printf("Enter password\n");
    
    while(1)
    {       
            c = getch();
            
            if(c == 13)
                 break;
            
            t++;
            strcat(input_pass,&c); // THIS IS THE PROBLEM I THINK
            gotoxy(t - 1, 1);
            printf("*");
    }
    
    r = strcmp(password,input_pass);
    
    if(r != 0)
    {
         printf("\n\nIncorrect password\n");
         goto done;
    }
    
    printf("\n\nCorrect!\n");
    
    done:
         
    getchar();
    return(0);
}

Your strcat() call certainly is the problem - strcat() needs to be passed two null-terminated strings. A single character won't do, as it will read past wherever that character is in memory until it accidentally reaches a null byte. Best bet is to keep track of how many characters have been entered and manually place them in your buffer. That way you can also make sure the buffer doesn't overflow.

Originally Posted by JohnGraham

Your strcat() call certainly is the problem - strcat() needs to be passed two null-terminated strings. A single character won't do, as it will read past wherever that character is in memory until it accidentally reaches a null byte. Best bet is to keep track of how many characters have been entered and manually place them in your buffer. That way you can also make sure the buffer doesn't overflow.

So, could I use strcpy and put the characters in input_pass? For the overflow problem, I could just change it to a for loop, and make it count to 10 before exiting the loop, or if break; has already been called.

Code:

char pass[11] = {0}
int x = -1;
 do 
  { x++;
  pass[x] = fgetc(stdin);
  printf("\b*");  
  } while ((x < 10) && (pass[x] !=\n));
  pass[x] = 0;

  if (strcmp(password,pass))
    exit(0);

That looks so much more confusing than it has to be...

Originally Posted by binks

That looks so much more confusing than it has to be...

Ok... then don't use it... no skin off my nose.

Could I use strcpy like so?

Code:

strcpy(input_pass, &c);

Or will strcpy not work for single character variables?

No. Did you try to compile it?

The "str" is a tip-off that it wants to operate on STRINGS - which really don't exist - they are really arrays of chars, terminated with a '\0' (null)

Originally Posted by quzah

Of course they do. They aren't their own unique data type called "string", but:That's a string.

Quzah.

In pretend-ville maybe... everywhere else it's just a specially formatted array of characters.

Originally Posted by binks

Could I use strcpy like so?

Code:

strcpy(input_pass, &c);

Or will strcpy not work for single character variables?

For single characters just use array[element] = character (despite it's name, that is a numerical assignment) ... strcpy() is going to go running rough shod all overy your program stack looking for a 0 to stop on.

You really should read up on "strings" in C... hit the books or grow on Google...

Originally Posted by quzah

Which would be a valid statement if we were on the "Everywhere Else Board".


Quzah.

Yeah but this ain't "pretend-ville" either...

LOL.