C++ Detect when user presses arrow key

Question

I have been having a problem with detecting arrow key presses in my C++ console application. I have tried everything I have found, both here and on other tutorial sites, but all of them give me the same thing whenever I press the arrow:

Process returned 0 <0x0> execution time : 2.249 s Press any key to continue. 

Here are all the methods of detecting the key press that I have tried, all ending up the same way. These are the only two left in my code, the others I attempted I deleted instead of commenting out.

Method one:

c1 = getch(); if(c1 == 0) {      c2 = getch();      if(c2 == 72) {cout << endl << "Up Arrow" << endl;}     else if(c2 == 80) {cout << endl << "Down Arrow" << endl;}     else{cout << endl << "Incorrect Input" << endl;}  } 

Method two:

switch(getch()) { case 65:        cout << endl << "Up" << endl;//key up     break; case 66:     cout << endl << "Down" << endl;   // key down     break; case 67:     cout << endl << "Right" << endl;  // key right     break; case 68:     cout << endl << "Left" << endl;  // key left     break; } 

Is there some error in my code which made me go back to my main method, or did it skip over some code? Is there a faster way to do this? I'm almost 100% sure that my other code doesn't have anything to do with this problem, because I isolated the code from be dependent on any other aspect of the program, and I kept having the same problem.

Again, I tried every method of getting the arrow key press that I could find, and I keep getting the same problem. If it matters, I'm on a Windows 8 Samsung ATIV Smart PC and using the keyboard dock.

Thanks in advance for any help.

Answer 1

#include <conio.h> #include <iostream> using namespace std;  #define KEY_UP 72 #define KEY_DOWN 80 #define KEY_LEFT 75 #define KEY_RIGHT 77  int main() {     int c = 0;     while(1)     {         c = 0;          switch((c=getch())) {         case KEY_UP:             cout << endl << "Up" << endl;//key up             break;         case KEY_DOWN:             cout << endl << "Down" << endl;   // key down             break;         case KEY_LEFT:             cout << endl << "Left" << endl;  // key left             break;         case KEY_RIGHT:             cout << endl << "Right" << endl;  // key right             break;         default:             cout << endl << "null" << endl;  // not arrow             break;         }      }      return 0; } 

output like this:

Up  Down  Right  Left  Up  Left  Right  Right  Up 

detected arrow key press!

Answer 2

The previous answer by arbboter is close but neglects the fact the arrow keys (and other special keys) return a scan code of two characters. The first is either (0) or (224) indicating the key is an extended one; the second contains the scan code value.

Without accounting for this, the ASCII values for "H", "K", "M", and "P" are misinterpreted as "Up", "Down", "Left", and "Right".

Here's a modified version of arbboter's code to demonstrate reading the extended value when one of the arrow keys is pressed:

#include <conio.h> #include <iostream> using namespace std;  #define KEY_UP    72 #define KEY_LEFT  75 #define KEY_RIGHT 77 #define KEY_DOWN  80  int main() {     int c, ex;      while(1)     {         c = getch();          if (c && c != 224)         {             cout << endl << "Not arrow: " << (char) c << endl;         }         else         {             switch(ex = getch())             {                 case KEY_UP     /* H */:                     cout << endl << "Up" << endl;//key up                     break;                 case KEY_DOWN   /* K */:                     cout << endl << "Down" << endl;   // key down                     break;                 case KEY_LEFT   /* M */:                     cout << endl << "Left" << endl;  // key left                     break;                 case KEY_RIGHT: /* P */                     cout << endl << "Right" << endl;  // key right                     break;                 default:                     cout << endl << (char) ex << endl;  // not arrow                     break;             }         }     }      return 0; }