How to simulate "Press any key to continue?"

Question

I am trying to write a C++ program in which when user enter any character from keyboard and it should move to next line of code.

Here is my code:

char c;

cin>>c;

cout<<"Something"<<endl;

but this is not working, because it only move to next line when I input some character and then press ENTER.

OR

If I use this

cin.get() or cin.get(c)

it move to next line of instruction when I press Enter.

But I wanted it to move to next line on any key pressed on the keyboard, how this can be done?

Answer 1

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

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

You could use the Microsoft-specific function _getch:

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

Answer 6

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

Answer 7

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.

Answer 8

If you're using Visual Studio 2012 or older, use the getch() function, if you are using Visual Studio 2013 or newer, use _getch(). You will have to use #include <conio.h>. Example:

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

int main()
{
   std::cout << "Press any key to continue. . .\n";
   _getch(); //Or getch()
}

Answer 9

This works on a Windows Platform: It Uses the Microprocessor registers directly and can be used to check key press or mousebutton

    #include<stdio.h>
    #include<conio.h>
    #include<dos.h>
    void main()
    {
     clrscr();
     union REGS in,out;
     in.h.ah=0x00;
     printf("Press any key : ");

     int86(0x16,&in,&out);
     printf("Ascii : %d\n",out.h.al);
     char ch = out.h.al;
     printf("Charcter Pressed : %c",&ch);
     printf("Scan code : %d",out.h.ah);
     getch();
    }

Answer 10

You can use the getchar routine.

From the above link:

/* getchar example : typewriter */
#include <stdio.h>

int main ()
{
  char c;
  puts ("Enter text. Include a dot ('.') in a sentence to exit:");
  do {
    c=getchar();
    putchar (c);
  } while (c != '.');
  return 0;
}

Answer 11

Another option is using threads with function pointers:

#include <iostream>
#include <thread> // this_thread::sleep_for() and thread objects
#include <chrono> // chrono::milliseconds()

bool stopWaitingFlag = false;

void delayms(int millisecondsToSleep) 
{
  std::this_thread::sleep_for(std::chrono::milliseconds(millisecondsToSleep));
}

void WaitForKey() 
{
  while (stopWaitingFlag == false)
  {
    std::cout<<"Display from the thread function"<<std::endl;
    delayms(1000);
  }
}

 

int main()
{
  std::thread threadObj(&WaitForKey);

  char userInput = '\0';
  while (userInput != 'y')
  {
    std::cout << "\e[1;31mWaiting for a key, Enter 'y' for yes\e[0m" << std::endl;
    std::cin >> userInput;
    if (userInput == 'y') {
      stopWaitingFlag = true;
    }
  }
  if (threadObj.joinable())
    threadObj.join();

  std::cout<<"Exit of Main function"<<std::endl;
  return 0;
}

Answer 12

Also you can use getch() from conio.h. Just like this:

...includes, defines etc
void main()
{
//operator
getch(); //now this function is waiting for any key press. When you have pressed its     just     //finish and next line of code will be called
}

So, because UNIX does not have conio.h, we can simulate getch() by this code (but this code already written by Vinary, my fail):

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

int mygetch( ) {
  struct termios oldt,
             newt;
  int            ch;
  tcgetattr( STDIN_FILENO, &oldt );
  newt = oldt;
  newt.c_lflag &= ~( ICANON | ECHO );
  tcsetattr( STDIN_FILENO, TCSANOW, &newt );
  ch = getchar();
  tcsetattr( STDIN_FILENO, TCSANOW, &oldt );
  return ch;
}

Answer 13

If you look up kbhit() function on MSDN now, it says the function is deprecated. Use _kbhit() instead.

#include <conio.h>
int main()
{
    _kbhit();
    return 0;
}

Answer 14

#include <iostream>
using namespace std;

int main () {
    bool boolean;
    boolean = true;

    if (boolean == true) {

        cout << "press any key to continue";
        cin >> boolean;

    }
    return 0;
}

Answer 15

Just use the system("pause"); command.

All the other answers over complicate the issue.