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

                 | for handles     | for pointers  |
                 | and numbers     |               |
| OS             | WPARAM          | LPARAM        |
|----------------|-----------------|---------------|
| 16-bit Windows | 16-bit unsigned | 32-bit signed |
| 32-bit Windows | 32-bit unsigned | 32-bit signed |
| 64-bit Windows | 64-bit unsigned | 64-bit signed |

The history of its definition has changed over the years.

WINDOWS.H (Windows 2.03 SDK, c. 1988)

/* Message structure */
typedef struct tagMSG {
    HWND hwnd;
    WORD message;
    WORD wParam;
    LONG lParam;
    DWORD time;
    POINT pt;
} MSG;

WinDefs.h (c. 1999)

/* Types use for passing & returning polymorphic values */
typedef UINT WPARAM;
typedef LONG LPARAM;
typedef LONG LRESULT;

WinDef.h (c. 2005)

/* Types use for passing & returning polymorphic values */
typedef UINT_PTR            WPARAM;
typedef LONG_PTR            LPARAM;
typedef LONG_PTR            LRESULT;

Bonus Reading

• What do the letters W and L stand for in WPARAM and LPARAM? ^archive (W is for unsigned 16-bit WORD, and L is for signed 32-bit LONG)
• What happens to WPARAM, LPARAM, and LRESULT when they travel between 32-bit and 64-bit windows? ^archive (the unsigned is zero-extended, the signed is sign-extended)