WPARAM and LPARAM parameters

Question

When passing a value to a function that takes both a WPARAM and a LPARAM parameter, does it matter on which of them I pass it? Someone told me that if I use Windows x64 I sh

Answer 1

When sending messages, WPARAM and LPARAM parameters have specific interpretations depending on the message. You need to pass those parameters in the way that the message that you are sending expects them to be passed. If you are defining your own message (perhaps via an offset from WM_USER, WM_APP, or RegisterWindowMessage), then you obviously have a bit more latitude.

In the days of 16-bit Windows, a WPARAM was a 16-bit word, while LPARAM was a 32-bit long. These distinctions went away in Win32; they both became 32-bit values.

According to this, LPARAM is defined as LONG_PTR, which in 64-bit Windows is a signed, 64-bit value. WPARAM is defined as UINT_PTR, which in 64-bit Windows is an unsigned, 64-bit value. If you are defining your own message, you might want to assign its parameters accordingly.