Question

I am trying to read a pasword and while I read it , display ** .

    cout << "\n Insert password : ";
loop1:
    string passw1 = "";
    char ch = _getch();
    while (ch != 13) // enter = char 13
    {
        if (!isalnum(ch))
        {
            cout << "\n\n Invalid character! Please insert the password again! ";
            goto loop1;
        }

        passw1.push_back(ch);
        cout << "*";
        ch = _getch();
    }

If I press for example , BACKSPACE , or SPACE or something that is not alpha-numerical , everything goes as planned. The problem is when I press any F key , or DELETE , HOME , INSERT , END , PG UP , PG DOWN , when the program crashes . Could you help me avoid the crash ? I would like to show an error message if an invalid key is pressed , not to have my program crash.

Answer 1

Use the is alphanumeric function – isalnum(char c ) to check if the parameter c is either a decimal digit
or an uppercase or a lowercase letter.

And then filter out characters less than 32 or higher than 122 like this : if (c > 32 && c <122) { Get_Password(); }

This MS Windows specific code below is not portable. For Linux/*NIX/BSD see this : Hide password input on terminal

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

int main()
{
    std::string password;
    char ch;
    const char ENTER = 13;

    std::cout << "enter the password:  ";

    while((ch = _getch()) != ENTER)
    {

        if (ch > 32 && ch<122)
        {
            if (isalnum(ch))
            {
                password += ch;
                std::cout << '*';

            }

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