How to simulate "Press any key to continue?"

Question

On Windows:

system("pause");

and on Mac and Linux:

system("read");

will output "Press any key to continue..." and obviously, wait for any key to be pressed. I hope thats what you meant

If you're on Windows, you can use kbhit() which is part of the Microsoft run-time library. If you're on Linux, you can implement kbhit thus (source):

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

int kbhit(void)
{
  struct termios oldt, newt;
  int ch;
  int oldf;

  tcgetattr(STDIN_FILENO, &oldt);
  newt = oldt;
  newt.c_lflag &= ~(ICANON | ECHO);
  tcsetattr(STDIN_FILENO, TCSANOW, &newt);
  oldf = fcntl(STDIN_FILENO, F_GETFL, 0);
  fcntl(STDIN_FILENO, F_SETFL, oldf | O_NONBLOCK);

  ch = getchar();

  tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
  fcntl(STDIN_FILENO, F_SETFL, oldf);

  if(ch != EOF)
  {
    ungetc(ch, stdin);
    return 1;
  }

  return 0;
}

Update: The above function works on OS X (at least, on OS X 10.5.8 - Leopard, so I would expect it to work on more recent versions of OS X). This gist can be saved as kbhit.c and compiled on both Linux and OS X with

gcc -o kbhit kbhit.c

When run with

./kbhit

It prompts you for a keypress, and exits when you hit a key (not limited to Enter or printable keys).

@Johnsyweb - please elaborate what you mean by "detailed canonical answer" and "all the concerns". Also, re "cross-platform": With this implementation of kbhit() you can have the same functionality in a C++ program on Linux/Unix/OS X/Windows - which other platforms might you be referring to?

Further update for @Johnsyweb: C++ applications do not live in a hermetically sealed C++ environment. A big reason for C++'s success is interoperability with C. All mainstream platforms are implemented with C interfaces (even if internal implementation is using C++) so your talk of "legacy" seems out of place. Plus, as we are talking about a single function, why do you need C++ for this ("C with classes")? As I pointed out, you can write in C++ and access this functionality easily, and your application's users are unlikely to care how you implemented it.

There is no completely portable solution.

Question 19.1 of the comp.lang.c FAQ covers this in some depth, with solutions for Windows, Unix-like systems, and even MS-DOS and VMS.

A quick and incomplete summary:

• You can use the curses library; call cbreak() followed by getch() (not to be confused with the Windows-specific getch()function). Note that curses generally takes control of the terminal, so this is likely to be overkill.
• You might be able to use ioctl() to manipulate the terminal settings.
• On POSIX-compliant systems, tcgetattr() and tcsetattr() may be a better solution.
• On Unix, you can use system() to invoke the stty command.
• On MS-DOS, you can use getch() or getche().
• On VMS (now called OpenVMS), the Screen Management (SMG$) routines might do the trick.

All these C solutions should work equally well in C++; I don't know of any C++-specific solution.

In windows, this short program accomplishes the goal: getch pauses the console until a key is pressed (https://www.geeksforgeeks.org/difference-getchar-getch-getc-getche/)

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

using namespace std;

void  check()
{
    char chk; int j;
    cout<<"\n\nPress any key to continue...";
    chk=getch();
    j=chk;
    for(int i=1;i<=256;i++)
      if(i==j) break;
    clrscr();
}

void main()
{
    clrscr();
    check();
    cout<<"\n\nIt works!";
    getch();
}

It should be noted that getch is not part of the standard library.

To achieve this functionality you could use ncurses library which was implemented both on Windows and Linux (and MacOS as far as I know).

I looked into what you are trying to achieve, because I remember I wanted to do the same thing. Inspired by Vinay I wrote something that works for me and I sort of understand. But I am not an expert, so please be careful.

I don't know how Vinay knows you are using Mac OS X. But it should work kind of like this with most unix-like OS. Really helpful as resource is opengroup.org

Make sure to flush the buffer before using the function.

#include <stdio.h>
#include <termios.h>        //termios, TCSANOW, ECHO, ICANON
#include <unistd.h>     //STDIN_FILENO


void pressKey()
{
    //the struct termios stores all kinds of flags which can manipulate the I/O Interface
    //I have an old one to save the old settings and a new 
    static struct termios oldt, newt;
    printf("Press key to continue....\n");

    //tcgetattr gets the parameters of the current terminal
    //STDIN_FILENO will tell tcgetattr that it should write the settings
    // of stdin to oldt
    tcgetattr( STDIN_FILENO, &oldt);
    //now the settings will be copied 
    newt = oldt;

    //two of the c_lflag will be turned off
    //ECHO which is responsible for displaying the input of the user in the terminal
    //ICANON is the essential one! Normally this takes care that one line at a time will be processed
    //that means it will return if it sees a "\n" or an EOF or an EOL
    newt.c_lflag &= ~(ICANON | ECHO );      

    //Those new settings will be set to STDIN
    //TCSANOW tells tcsetattr to change attributes immediately. 
    tcsetattr( STDIN_FILENO, TCSANOW, &newt);

    //now the char wil be requested
    getchar();

    //the old settings will be written back to STDIN
    tcsetattr( STDIN_FILENO, TCSANOW, &oldt);

}


int main(void)
{
  pressKey();
  printf("END\n");
  return 0;
}

O_NONBLOCK seems also to be an important flag, but it didn't change anything for me.

I appreciate if people with some deeper knowledge would comment on this and give some advice.

You could use the Microsoft-specific function _getch:

#include <iostream>
#include <conio.h>
// ...
// ...
// ...
cout << "Press any key to continue..." << endl;
_getch();
cout << "Something" << endl;