C++ password input on BOTH WINDOWS AND LINUX

[cshong]

I want to write a simple command line password input program. When the user input a password, the program must display "*" to cover the password, or do something to hide the password.

I want to compile my program on both Windows XP and Linux, PREFERABLY WITH EXACTLY THE SAME SOURCE CODES.

How to do this?

[jsmith]

Since terminal control differs drastically between Windows and Unix, you are left only with using a cross-platform GUI kit such as Qt.

I assume

#ifndef WINDOWS
// do this
#else
// do that
#endif

is out of the question.

[cshong]

Sorry, I forgot to tell that the program is a command line program with no GUI.

[Dufresne]

You can use conio.h libray for it.
Example :

#include <iostream>
#include <cstdlib>
#include <conio.h>

using namespace std ;

int main( void )
{
 	char ch ;
 	do{
	   	 ch = getch();
	   	 if( !iscntrl( ch ) )
	   	 	 putch( '*' );
	}while( ch != '\r' );
 	system( "PAUSE" );
 	return ( 0 );	
}

You can improve this example.

[jsmith]

Well, ...

conio.h does not exist in Linux. And getch() exists only in curses; putch() does not exist at all.

[Duthomhas]

You are trying to do something that is platform-dependent with the same code on every platform. By definition that can't be done.

The simplest answer is to simply turn off echo.

On Windows

#include <windows.h>

void echo( bool on = true )
  {
  DWORD  mode;
  HANDLE hConIn = GetStdHandle( STD_INPUT_HANDLE );
  GetConsoleMode( hConIn, &mode );
  mode = on
       ? (mode |   ENABLE_ECHO_INPUT )
       : (mode & ~(ENABLE_ECHO_INPUT));
  SetConsoleMode( hConIn, mode );
  }

On POSIX (Unix, Linux, etc)

#include <termios.h>
#include <unistd.h>

void echo( bool on = true )
  {
  struct termios settings;
  tcgetattr( STDIN_FILENO, &settings );
  settings.c_lflag = on
                   ? (settings.c_lflag |   ECHO )
                   : (settings.c_lflag & ~(ECHO));
  tcsetattr( STDIN_FILENO, TCSANOW, &settings );
  }

You will have to link with one of -lcurses or -ltermios or -lncurses ... whichever is appropriate for your system.

Now, you can turn echo on or off easily

#include <iostream>
using namespace std;

#include "platform-code.hpp"

int main()
  {
  string pwd;
  cout << "Please enter a passcode> ";

  echo( false );
  getline( cin, pwd );
  echo( true );

  cout << "\nYour password is \"" << pwd << "\"\n";
  return 0;
  }

When you compile and link, compile the platform-dependent code that is appropriate for your platform: the windows stuff on windows and the POSIX stuff on Unix/Linux/whatever. If you have other platforms in mind, you will have to write code appropriate for that too. Then link the module into the final executable.

Hope this helps.

[edit] BTW, I didn't test any of this code -- errors may have occurred.