How should we manage the Memory of the parameters passed by OS in WindowProc

Harshithraj1871 1,556

Hi,

Im working in Win32 desktop application in cpp.

When a Window Proc is triggered with some WM_* msg, We may receive some LPARAM and WPARAM data. These parameters are different concerning the MSG passed. This can hold variable-length data like pointers to strings, structs, or class objects.

Suppose I want to do some ASYNC operation on some WM_* while passing the LPARAM, and WPARAM to it and let the OS continue its work. Should I pass the LPARAM, and WPARAM to the ASYNC operation by value or by reference? Which is the best practice?

RLWA32 46,376 Reputation points

2024-12-30T11:26:29.74+00:00

I don't think it is safe to assume that any parameter contained in the WPARAM or LPARAM of a windows message would be valid outside of the application's window procedure.

Can you give a specific example of what you want to accomplish with an actual window message?
Harshithraj1871 1,556 Reputation points

2024-12-30T12:30:20.9166667+00:00

Consider WM_SETTINGCHANGE, here in LPARAM we will receive string. I want to pass it asynchronously and let the main thread continue its work. Should I pass it by reference or by value? which is the best practice?
Harshithraj1871 1,556 Reputation points

2024-12-30T17:44:06.1233333+00:00

Thank you, It was helpful

Accepted answer

Darran Rowe 1,321 Reputation points

2024-12-30T12:39:29.02+00:00

Neither, copy the string.

Windows only guarantees the existance of the backing memory until SendMessage/DispatchMessage returns.
Please sign in to rate this answer.

1 person found this answer helpful.

0 comments No comments
Sign in to comment

Use comments to ask for clarification, additional information, or improvements to the question.

Share via

How should we manage the Memory of the parameters passed by OS in WindowProc

0 additional answers

Your answer