Blank_Struct function [Revelation On-Line Wiki]

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====== Blank_Struct function  ======


 
==== Description ====
 
Builds a blank structure to pass to a DLL which will then fill in the structure's elements.
 
==== Syntax ====
 
//struct// = **Blank_Struct**(//structname//)
 
==== Parameters ====
 
Many DLL functions, including some in the Windows API, take a pointer to a structure as an argument and use that pointer to set values in the structure. To call one of these functions, prototype the parameter as being LPCHAR (meaning a pointer to the first byte of something) and use Blank_Struct to generate a blank structure for the function to fill.

The structure definition must be pre-defined using the [[define_struct|Define_Struct routine]].  The RECT struct for the example below is defined as follows:

{{{guides:programming:programmers_reference_manual:rectstruct.gif?372x353}}
 

 
==== See Also ====
 
[[build_struct|Build_Struct()]], [[define_struct|Define_Struct]], [[struct_len|Struct_Len()]], [[var_to_struct|Var_To_Struct()]], [[parse_struct|Parse_Struct]], [[chapter_dll|Chapter 7: Calling DLL Functions from Basic+]]
 
==== Example ====
 
<code>
* assumes the structure called RECT has been defined as
* above and the API function GetWindowRect has been defined in
* DLL_USER32 (the 32 bit DLL) as:
* VOID STDCALL GetWindowRect(HANDLE, LPCHAR)

declare function Get_Property, Blank_Struct

declare subroutine Parse_Struct, GetWindowRect

 

hwnd = Get_Property(@window , 'HANDLE')

rect = Blank_Struct('RECT')

GetWindowRect(hwnd, rect)

Parse_Struct (rect, 'RECT', left, top, right, bottom)
</code>