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Reading Scan Codes from the Keyboard

nanodano nanodano is offline Offline May 25th, 2006, 2:51 am |
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Introduction

Hello everyone. This little code snippet shows you how to read in scan codes from the keyboard. It is slightly different than reading in a regular character. When you use the getch() function, it is normally returning an ASCII value. Some keyboards have extra keys though. These include the F1 - F12 function keys and the directional arrows to start. These keys do not have an ASCII code. A char data type is a one byte item. When you press a key that doesn't have an ASCII code, it returns two bytes. If the first byte is 0, then the next byte contains the scan code. In the following code, I include the scan code for many typical keys and how to read them.

Notes:
  • Even though there are two calls to getch(), it does not require two keystrokes.
  • Not all of these scan codes may be 100% accurate for all computers. It may, of course, need some modifications.

C Syntax (Toggle Plain Text) 
  1. /* This program shows how to pick up the scan codes from a keyboard */
  2.  
  3. /* These define the scan codes(IBM) for the keys. All numbers are in decimal.*/
  4. #define PAGE_UP     73
  5. #define HOME        71
  6. #define END         79
  7. #define PAGE_DOWN   81
  8. #define UP_ARROW    72
  9. #define LEFT_ARROW  75
  10. #define DOWN_ARROW  80
  11. #define RIGHT_ARROW 77
  12. #define F1          59
  13. #define F2          60
  14. #define F3          61
  15. #define F4          62
  16. #define F5          63
  17. #define F6          64
  18. #define F7          65
  19. #define F8          66
  20. #define F9          67
  21. #define F10         68
  22. #include <iostream>
  23. #include <conio.h>
  24.  
  25. using namespace std;
  26.  
  27. void main()
  28. {
  29. 	char KeyStroke;
  30.  
  31. 	cout << "Press Escape to quit." << endl;
  32.  
  33. 	do
  34. 	{
  35. 		KeyStroke =	getch();
  36.  
  37. 		if (KeyStroke == 0)
  38. 		{
  39. 			KeyStroke = getch(); // Even though there are 2 getch() it reads one keystroke
  40. 			switch (KeyStroke)
  41. 			{
  42. 			case PAGE_UP:
  43. 				cout << "PAGE UP" << endl;
  44. 				break;
  45. 			case PAGE_DOWN:
  46. 				cout << "PAGE DOWN" << endl;
  47. 				break;
  48. 			case HOME:
  49. 				cout << "HOME" << endl;
  50. 				break;
  51. 			case END:
  52. 				cout << "END" << endl;
  53. 				break;
  54. 			case UP_ARROW:
  55. 				cout << "UP ARROW" << endl;
  56. 				break;
  57. 			case DOWN_ARROW:
  58. 				cout << "DOWN ARROW" << endl;
  59. 				break;
  60. 			case LEFT_ARROW:
  61. 				cout << "LEFT_ARROW" << endl;
  62. 				break;
  63. 			case RIGHT_ARROW:
  64. 				cout << "RIGHT_ARROW" << endl;
  65. 				break;
  66. 			case F1:
  67. 				cout << "F1" << endl;
  68. 				break;
  69. 			case F2:
  70. 				cout << "F2" << endl;
  71. 				break;
  72. 			case F3:
  73. 				cout << "F3" << endl;
  74. 				break;
  75. 			case F4:
  76. 				cout << "F4" << endl;
  77. 				break;
  78. 			case F5:
  79. 				cout << "F5" << endl;
  80. 				break;
  81. 			case F6:
  82. 				cout << "F6" << endl;
  83. 				break;
  84. 			case F7:
  85. 				cout << "F7" << endl;
  86. 				break;
  87. 			case F8:
  88. 				cout << "F8" << endl;
  89. 				break;
  90. 			case F9:
  91. 				cout << "F9" << endl;
  92. 				break;
  93. 			case F10:
  94. 				cout << "F10" << endl;
  95. 				break;
  96. 			default:
  97. 				cout << "Some other key." << endl;
  98. 			}
  99. 		}
  100. 		else
  101. 			cout << KeyStroke << endl;
  102. 	} 
  103. 	while (KeyStroke != 27); // 27 = Escape key
  104. }
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Code Snippet
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C Syntax
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  1. A simple program that shows you how to read the keyboard scan code for keys that don't have a normal ASCII code. It includes typical scan codes for the function keys and and the arrow keys.
  2.  
Code Snippet Comments
1
viper33m viper33m is offline Offline | Apr 14th, 2008
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One modification for those under vista/visual 2008:

C Syntax (Toggle Plain Text) 
  1. KeyStroke =getch();
  2. if (KeyStroke == -32)  //weird, i know.... but it works
  3. {
  4. 	KeyStroke = getch();
  5. ...}
thk you for the ideea. :hat off:
 
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ramthegreatcv ramthegreatcv is offline Offline | 31 Days Ago
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thanks a lot..

C Syntax (Toggle Plain Text) 
  1. if (KeyStroke == -32)

works on DevC++ Windows XP.
 
-1
marco93 marco93 is offline Offline | 30 Days Ago
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This "code" has no sense at all (case, case, case... horrible !!!!)
It's done in 1 line of code with Win32 api (VK)
 
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ramthegreatcv ramthegreatcv is offline Offline | 30 Days Ago
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@macro93 can u please explain how it can be done using Win32 api?
 
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Ancient Dragon Ancient Dragon is offline Offline | 30 Days Ago
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win32 api doesn't work on non-Windows platforms, but this code snippet will work with some possible mods to the defines at the top.
 
 

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