how to get the last key pressed without stopping the programm ?

[WARburg]

Hello Everyone!
That's my first post on this forum and I'd like to greet Everyone

I got a question about getting the last key pressed without stopping the programm. I know that getchar(), cin, getch() commands don't allow to do that. Have You any idea how to solve this problem?

I 'd like to do sth like that:

while(play){
char a;
a=get_last_key_without_stopping_the_programm(); // Do You know a function similiar to that?
switch(a){
case: 'W' :
do_sth();
break;
case 'S' :
do_sth_else();
break;
default:
do_default();
break;
}
a='*';
}

[Narue]

>I know that getchar(), cin, getch() commands don't allow to do that.
getch (and getche) does, but it isn't a standard function and won't exist on all implementations. What compiler and operating system do you use?

[Emmitt310]

Well, i think i know what you mean but it may help to know what kind of program you want to make. If it's a win32 application, checking for keyboard input during a loop is easy, but if this isnt a win32 application, keyboard input can still be checked, its just a bit more complicated.

[mango_maniac]

Well, i think i know what you mean but it may help to know what kind of program you want to make. If it's a win32 application, checking for keyboard input during a loop is easy, but if this isnt a win32 application, keyboard input can still be checked, its just a bit more complicated.

First post here...I found this site looking for similar information. I'm using win32, but am totally unfamilliar with the windows.h header. I currently only know standard c++. How would one go about capturing keystrokes without waiting for <return> to be pressed. If you could demonstrate a compilable snippet, I'd be grateful.

MM

[Emmitt310]

Ok well, the reason why it's easy in win32 to check for keyboard input is because you can check for a window message WM_KEYDOWN. Each key has a specific virtual key code, but, you can figure that out. Heres a simple code snippet that checks for if the key pressed was the esc key. (this is compilable if you know where to put it in your program)

switch(message)
{
     case WM_KEYDOWN:
          switch(wParam)
          {
               case VK_ESCAPE: //the virutal key code for esc
                    PostQuitMessage(0);
               break;
          }
     break;
     /*
     rest of the window procedure
     */
}

[mango_maniac]

Ok well, the reason why it's easy in win32 to check for keyboard input is because you can check for a window message WM_KEYDOWN. Each key has a specific virtual key code, but, you can figure that out. Heres a simple code snippet that checks for if the key pressed was the esc key. (this is compilable if you know where to put it in your program)

switch(message)
{
     case WM_KEYDOWN:
          switch(wParam)
          {
               case VK_ESCAPE: //the virutal key code for esc
                    PostQuitMessage(0);
               break;
          }
     break;
     /*
     rest of the window procedure
     */
}

Thanks for your help. I ended up doing it another way. I'm going to use something like the following. Do you see problems other than non-portability to systems that don't use ascii 13 for <return>?

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

using namespace std;

string getPassword();

int main(){
    
    string password("true");
    
    while (true){
        
        cout << " Input Password: ";
        password = getPassword();
        
        cout << "Verify Password: ";
        string pwverify = getPassword();
        
        if(password == pwverify) {break;}
        cout << "\nPassword mismatch.  Try again\n";
    }
    
    cout  << password << endl << password.size() << endl;
    
    system("pause");      
} 


string getPassword(){ 
    CHAR buffer[1] = ""; 
    DWORD w; 
    HANDLE console = GetStdHandle(STD_OUTPUT_HANDLE); 
    HANDLE keyboard = GetStdHandle(STD_INPUT_HANDLE); 
    INPUT_RECORD input[1]; 
    
    string pw;
    
     while(true) { 
        // Read an input record. 
        ReadConsoleInput(keyboard, input, 1, &w); 
         
        // Process a key down input event. 
        if(input[0].EventType == KEY_EVENT 
           && input[0].Event.KeyEvent.bKeyDown)
        { 
         
            // Retrieve the character that was pressed. 
            buffer[0] = input[0].Event.KeyEvent.uChar.AsciiChar; 
            
            if(buffer[0] == 13){ break;}  // enter pressed
            if(buffer[0] == 8){           // backspace
                pw.erase(pw.size()-1, 1);
                cout << "\b \b";
                continue;
            }
            
            if(buffer[0] != 0) {  // 0 is function keys, shift, ctrl, etc.
               cout << '*';
               pw += buffer[0];
            }
        } 
    }
    cout << endl;
    return pw;
}

[WARburg]

>I know that getchar(), cin, getch() commands don't allow to do that.
getch (and getche) does, but it isn't a standard function and won't exist on all implementations. What compiler and operating system do you use?

I use Linux and Windows OS both and I'd like to make an application that is compatible with both of them(or needs just a few little changes). I try to make some snake-similar game in ASII. Compiler for Windows I use is Borland c++ builder 6.0 and for Linux g++).

[Quetzalcoatl]

How would I do a similar thing using TC(required for school), which cannot use Windows.h? (Uses DOS)

[Marcosp]

About the solution given by Mango Maniac, does anyone knows how to do the same but using a Matlab mex file? I runned a modified version of his program in Visual C++ and it worked, but when I put the same code in the Matlab "mexfuction" the program compile and runs, but it doesn't respond when I press the keys. Here is the code:

#include <windows.h> 
#include <string>
#include <iostream>
#include <stdio.h>
#include "C:\MATLAB7\extern\include\mex.h"

CHAR buffer[1] = "";
DWORD w; 
HANDLE console = GetStdHandle(STD_OUTPUT_HANDLE); 
HANDLE keyboard = GetStdHandle(STD_INPUT_HANDLE); 
INPUT_RECORD input[1];

void mexFunction(int nlhs, mxArray *plhs[],int nrhs, const mxArray *prhs[]) {


    mexPrintf("para cima");
    while (1) {
        ReadConsoleInput(keyboard, input, 1, &w);
        if(input[0].EventType == KEY_EVENT && input[0].Event.KeyEvent.bKeyDown) {                                                
            buffer[0] = input[0].Event.KeyEvent.uChar.AsciiChar;
            if(buffer[0] == 13) { break;}
            if(buffer[0] == 56) {mexPrintf("para cima");}
            if(buffer[0] == 50) {mexPrintf("para baixo");}
            if(buffer[0] == 52) {mexPrintf("esquerda");}
            if(buffer[0] == 54) {mexPrintf("direita");}

            }
    }
}

I'm using a windows XP, Matlab 7 and Visual C++ 6.0

[pteryx]

The advice by Warburg is a valuable hint, but the WIN32 API funcion ReadConsoleInput waits for a keypress or a mouseclick. It must be supplemented with a wait function. The following function returns zero when nothing was pressed and ASCII code when something "ASCII" was pressed. I hope that this solution really works (even in "console" applications), but nothing is 100% ...

int keytest( void )
{
    CHAR ch;
    DWORD dw;
    HANDLE keyboard;
    INPUT_RECORD input;

    keyboard = GetStdHandle(STD_INPUT_HANDLE);

    dw = WaitForSingleObject( keyboard, 0 );
    if( dw != WAIT_OBJECT_0 )
      return 0;
    dw = 0;
    // Read an input record.
    ReadConsoleInput(keyboard, &input, 1, &dw);

    ch = 0;
    // Process a key down input event.
    if( !(     input.EventType == KEY_EVENT
            && input.Event.KeyEvent.bKeyDown )  )
    {
        return 0;
    }


    // Retrieve the character that was pressed.
    ch = input.Event.KeyEvent.uChar.AsciiChar;

    // Function keys filtration
    if( input.Event.KeyEvent.dwControlKeyState &
        ( LEFT_ALT_PRESSED | LEFT_CTRL_PRESSED | RIGHT_ALT_PRESSED | 
          RIGHT_CTRL_PRESSED )
      )
      return 0;

    // if( ch == 13 )
    //  ...;  // enter pressed

    return ch;
}

[zeroliken]

The advice by Warburg is a valuable hint, but the WIN32 API funcion ReadConsoleInput waits for a keypress or a mouseclick. It must be supplemented with a wait function. The following function returns zero when nothing was pressed and ASCII code when something "ASCII" was pressed. I hope that this solution really works (even in "console" applications), but nothing is 100% ...

int keytest( void )
{
    CHAR ch;
    DWORD dw;
    HANDLE keyboard;
    INPUT_RECORD input;

    keyboard = GetStdHandle(STD_INPUT_HANDLE);

    dw = WaitForSingleObject( keyboard, 0 );
    if( dw != WAIT_OBJECT_0 )
      return 0;
    dw = 0;
    // Read an input record.
    ReadConsoleInput(keyboard, &input, 1, &dw);

    ch = 0;
    // Process a key down input event.
    if( !(     input.EventType == KEY_EVENT
            && input.Event.KeyEvent.bKeyDown )  )
    {
        return 0;
    }


    // Retrieve the character that was pressed.
    ch = input.Event.KeyEvent.uChar.AsciiChar;

    // Function keys filtration
    if( input.Event.KeyEvent.dwControlKeyState &
        ( LEFT_ALT_PRESSED | LEFT_CTRL_PRESSED | RIGHT_ALT_PRESSED | 
          RIGHT_CTRL_PRESSED )
      )
      return 0;

    // if( ch == 13 )
    //  ...;  // enter pressed

    return ch;
}

you do realize your replying to a post from 2005