wParam and lParam

[h9uest]

This question refers to the MSG structure. See below for the structure:
http://msdn.microsoft.com/en-us/library/ms644958%28VS.85%29.aspx

typedef struct tagMSG {
  HWND   hwnd;
  UINT   message;
  WPARAM wParam;
  LPARAM lParam;
  DWORD  time;
  POINT  pt;
} MSG, *PMSG, *LPMSG;

My question:
What's the difference between wParam and lParam? What do the 'w' and 'l' before param stand for?

I know they are additional messages and I think I know what it means by the general term "additional message". The heart of my question is their difference. It's probably not important from a pragmatic point of view since we don't usually need to deal directly with them, but I just want to know, for curiosity.

Thanks for any input.

[webJose]

I believe the names come from 16-bit development and no longer have meaning, but the names were kept. They both are 4 or 8 bytes in size in 32-bit and 64-bit development respectively. More than that I don't remember.

[h9uest]

@ webJose:
Thank you very much for the reply! You are right.

I've also looked it up around and finally found it in a win32 book. I'll summarize it for other people in the future who run into the same confusion as I did:

In addition to webJose's comment: (assuming 32 bit machine)
wParam and lParam are used differently across messages. For example, WM_CLOSE doesn't use any and WM_COMMAND uses both in the way that:
wParam (32 bit, 2 words: high-bit word HIWORD and low bit word LOWORD) stores message in HIWORD and stores the control that sends the message in LOWORD;
lParam stores the window handle to the control which sent the message (of course, if message isn't from a control, lParam is NULL)


To sum up, they're usually hidden from a programmer who uses Win API. We don't typically deal with them directly.

[modoran]

To sum up, they're usually hidden from a programmer who uses Win API. We don't typically deal with them directly.

You are wrong, every Win Api program deals with lParam and wParam directly in main message loop.