Thread: Login program

Originally Posted by cpjust

Why not? getchar() reads a character from the keyboard and prints it to the screen. getch() only does half the work, so you'd think it would be easier to implement than getchar().

That's not entirely true. In general, this is more how it actually works:

getchar() simply reads the char from the buffer of the FILE *. If you don't have anything in the buffer to read, the OS-specific read function is called. The printing of the char to the screen is NOT done by getchar(). That is done by your shell/OS read function/etc. etc..

The default behavior of your system is to echo chars from beyond stdin into the screen. Think about it for a second. The chars are being printed to the screen BEFORE it's even accepted by stdin (because stdin actually wraps the OS version of stdin).

Functions like getch() actually change the terminal settings so echoing is NOT done in this manner. On Windows this is done with SetConsoleMode() I believe. For *nix systems you have to similarly play with the settings and have it so the output is not echoed to stdout.

In fact, I think both Windows and *nix systems allow you to preserve the terminal settings. You might be able to write a program which changes your terminal mode, quits, and then you could start another program which uses the new terminal mode where getchar() would behave like getch().

Heres the program to accept a password.While typing the characters are masked using '*' character.It also accepts backspace.Displays the entered pw when user hits ENTER key

heres the program:
check out:
http://www.lern2hack.blogspot.com/20...d-mask-it.html

Originally Posted by sriki

Heres the program to accept a password.While typing the characters are masked using '*' character.It also accepts backspace.Displays the entered pw when user hits ENTER key

heres the program:
check out:
http://www.lern2hack.blogspot.com/20...d-mask-it.html

Sweet! Non-indented code that doesn't compile(VC2008)!

Oh look, sriki is back pushing his hacker wannabe site with dubious code full of mistakes.
Tell me, what happens when I type in 30000 characters into your "program" ?
More like a "how to write code which makes it easy to be hacked" site IMO.

Not to mention it's so poorly written. if (ch == 13) <--- OK, how the heck am I supposed what ASCII value 13 is?
sriki: It's fine to teach other how to do things, but please, avoid poor programming concepts and things. If you're going to teach someone, do it right! There's enough of bad programming examples out there - we don't need more of them!

That is horrible code.

What I posted should work on Windows. I believe someone might have posted something similar for *nix systems somewhere else here (in the C++ section perhaps).

Here's my version (based on MacGyver's getch() function):

Code:

/* prototypes */
char mygetch(void);
void getpassword(char password[], int maxlength);

/* input password from user */
void getpassword(char password[], int maxlength)
{
	int i=0, done=0;
	char c;

	printf("Please input password (max. %d characters): ", maxlength);
	fflush(stdout);

	while (!done)
	{
		c = mygetch();
		switch(c)
		{
			case '\r':
			case '\n':
				done = 1;
				break;
			case '\b':
				if (i > 0)		/* perform backspace only if characters have already been input */
				{
					printf("\b \b");
					i--;
				}
				break;
			default:
				if (i<maxlength && isprint(c))	/* save character in password as long as it's not a none-printing character */
				{
					password[i++] = c;
					putchar('*');
				}
				break;
			}
		fflush(stdout);
	}
	password[i] = '\0';
}

/* like getchar() except without echo */
char mygetch(void)
{
  static HANDLE hIn;
  static DWORD  NumRead;
  static INPUT_RECORD InRec;
  static char c;

  hIn = GetStdHandle(STD_INPUT_HANDLE);
  if(hIn == INVALID_HANDLE_VALUE)
  {
    printf("GetStdHandle poop");
  }
  else
  {
    do
    {
      ReadConsoleInput(hIn, &InRec, 5, &NumRead);
      if (InRec.EventType == KEY_EVENT)
      {
        if (InRec.Event.KeyEvent.bKeyDown == 1)
        {
          c = InRec.Event.KeyEvent.uChar.AsciiChar;
          /* testing print
          printf("  KDown  Repeat  KeyCode  ScanCode  Unicode  Ascii  Ctrl-State \n");
          printf("  %3x    %3x     %3x      %3x       %3x      %3x    %3lx \n",
                  InRec.Event.KeyEvent.bKeyDown,
                  InRec.Event.KeyEvent.wRepeatCount,
                  InRec.Event.KeyEvent.wVirtualKeyCode,
                  InRec.Event.KeyEvent.wVirtualScanCode,
                  InRec.Event.KeyEvent.uChar.UnicodeChar,
                  InRec.Event.KeyEvent.uChar.AsciiChar,
                  InRec.Event.KeyEvent.dwControlKeyState );
          */
          /* printf("|if %c %02x ", c, c);  testing*/
          break;
        }
      }
    }
    while( c !=  '\r' );
  }
  return c;
}

Thanks to all the people who helped me out with it (from this forum)

Code:

Error	1	error C2065: 'KEYLENGTH' : undeclared identifier

You probably meant to put maxlength there.

Sure, I suppose you can ignore the prototypes, I guess.