Handling 32-Bit Messages

Handles grow to 32 bits under Win32, so they can no longer be combined with other information and still fit into a 32-bit parameter (lParam). The handle now occupies all of lParam, so information formerly in the high or low word of lParam must now move to wParam.

Because the wParam message parameter also grows to 32 bits, it can hold the information that can no longer be held in lParam.

This figure illustrates how the parameter sizes change, and how information is repacked for WM_COMMAND, one of the messages affected.

Parameter Sizes

See the following topics on handling 32-bit messages:

• Extracting Data from Messages with Portable Code
  
  
• Using Proper Data Types