Replacement to getch based code block in cpp

There is no standard replacement in C++.

Linux (and similar systems such as BSD), there is a legacy function getpass whose use is not recommended. I mention it because the documentation of that function in glibc suggests following:

This precise set of operations may not suit all possible situations. In this case, it is recommended that users write their own getpass substitute. For instance, a very simple substitute is as follows:

#include <termios.h>
#include <stdio.h>

ssize_t
my_getpass (char **lineptr, size_t *n, FILE *stream)
{
  struct termios old, new;
  int nread;

  /* Turn echoing off and fail if we can’t. */
  if (tcgetattr (fileno (stream), &old) != 0)
    return -1;
  new = old;
  new.c_lflag &= ~ECHO;
  if (tcsetattr (fileno (stream), TCSAFLUSH, &new) != 0)
    return -1;

  /* Read the passphrase */
  nread = getline (lineptr, n, stream);

  /* Restore terminal. */
  (void) tcsetattr (fileno (stream), TCSAFLUSH, &old);

  return nread;
}

Note that the example is written in C, and is not valid C++. Small changes are required, in particular there is a C++ keyword new being used as a variable name. Simply rename it to something else.

Also note that the behaviour is to not echo at all, rather than echo *. This is conventional in POSIX systems, and safer because the it does not reveal the length of the passphrase.