Resolved I would like to have only one API declare

[aaaron123@roadrunner.com]

Public Declare Auto Function SendMessage Lib "user32.dll" (hWnd As IntPtr, msg As Integer, wParam As IntPtr, lParam As IntPtr) As IntPtr
Public Declare Auto Function SendMessage Lib "user32.dll" (hWnd As IntPtr, msg As Integer, wParam As IntPtr, lParam As Integer) As IntPtr

This is old 32-bit code that still works with 64-bits.
But since integer and IntPtr are equal in size only at 32 bits and not at 64 bits I wonder why.
Integers and floating-point numbers, are blittable and do not require marshalling.
I have not been able to learn the default marshalling of Intptr.

Can you explain why passing a 32-bit and a 64-bit both work?

I would like to have only one declare and compensate at the calls.
Can you suggest which would be the better choice?

 

[JohnH]

IntPtr as pointer is correct for both bitness, but it can be convenient to pass the lparam additional info directly, for example an enum value or constant or a string. A declare with lparam as String (input) or StringBuilder (output) is common.

 

[aaaron123@roadrunner.com]

I'm thinking now that Integers must get marshalled to 64-bit if the API is 64-bit. Correct?

Isn't the API's stack a set of 64-bit values? I read, and nentioned above, that it integers did not need marshalling but it seems to me the API would expect 64 correct bits.

but it can be convenient to pass the lparam additional info directly

I want to be sure I understand this. I take this to mean it can be convenient to retain both declares. And if neaded, some with lparam as appropiate.

 

[JohnH]

SendMessage function (winuser.h) - Win32 apps

Sends the specified message to a window or windows. The SendMessage function calls the window procedure for the specified window and does not return until the window procedure has processed the message. (SendMessageW)

learn.microsoft.com

Windows Data Types (BaseTsd.h) - Win32 apps

The data types supported by Windows are used to define function return values, function and message parameters, and structure members.

learn.microsoft.com

Windows data type is LPARAM, which is alias for LONG_PTR, a "signed long type for pointer precision" that is bitness-dependent.
For some windows messages that is a just a 32 bit integer or a string reference in/out anyways.

 

[JohnH]

If you're doing lots of P/Invoke, consider using the Vanara libraries where most declarations is covered already, the libraries also has helper methods for some common operations. GitHub - dahall/Vanara: A set of .NET libraries for Windows implementing PInvoke calls to many native Windows APIs with supporting wrappers.