How Do Keyboard Scan Codes Work with Modified Keys like 'Alt' or 'Ctrl'?

[aychamo]

Hey guys;

I was driving the other night, and I was thinking about some programs I used to write many years ago in Pascal (like ~ 11-12 years ago in TurboPascal 7.0, or was it 6.0?) in which I used to catch the keyboard scan codes.

I realized that I neve caught a keyboard scan code for a key that was modified with "Alt" or "Ctrl". I remember for an arrow key you would check for (0 + 75) or something. How would you check the keyboard "buffer" for presence of a key which is modified with Alt or Ctrl?

Also, would, say, "Alt-F4" be a single keyboard scan code, or would the keyboard interpret it as mulitple keypresses?

I'm just curious :)

 

[TenaliRaman]

http://www.jpsoft.com/help/index.htm?keyscanexpl.htm

If u have any doubts here post back and i will try to clarify.

 

[ravenprp]

Hi there,

That's a great question! Keyboard scan codes can definitely be tricky to work with, especially when it comes to modified keys like "Alt" or "Ctrl". The reason you may not have caught a keyboard scan code for a modified key is because these keys are not considered as separate keys by the operating system. Instead, they are modifiers that change the behavior of other keys when pressed in combination.

To check for the presence of a key modified with "Alt" or "Ctrl", you would need to use a different approach. One way to do this would be to use the GetAsyncKeyState function in Windows, which allows you to check the state of a specific key at any given time. This function returns a bit flag indicating whether the key is currently pressed or not, and you can use this to determine if a modified key is being pressed along with another key.

As for your second question, "Alt-F4" would not be a single keyboard scan code. It would be interpreted as two separate keypresses - "Alt" and "F4". This is because the "Alt" key is a modifier and does not have its own scan code. It simply modifies the behavior of the "F4" key, which would have its own scan code.

I hope this helps answer your questions and satisfy your curiosity! Let me know if you have any further questions or need clarification on anything. Happy coding!