Navigation:  Tutorial > Using Peek...() and Poke...() functions

We can start building a small example to retrieve the bounding rectangle of the windows desktop. In user32.dll we can found 2 functions that we can use to retrieve this info. GetDesktopWindow() to retrieve the numeric handle to the desktop window and GetWindowRect() to retrieve the bounding rectangle.

 

 

#include "ot4xb.ch"

#include "dll.ch"

proc main() ... return

 

function aGetDesktopRect( lOk )

local cRect := ChrR( 0 , 16) // Same as Replicate(Chr(0),16)

 

ot4xb peek and poke functions work with numeric memory pointers or also with Xbase++ character buffers, in this case we are going to use a character buffer to avoid the allocation a release steps.

 

local hDesktop  

local nShift

local aRect := NIL

 

// Retrieve the handle to the desktop window

hDesktop :=  DllCall( "user32" , DLL_STDCALL ,"GetDesktopWindow");

// Fill cRect with GetWindowRect()

lOk := ( DllCall("user32",DLL_STDCALL,"GetWindowRect",hDesktop,@cRect) != 0 )

if lOk

   aRect  := Array(4)

   nShift := 0   

 

At every call to any ot4xb peek or poke function nShift will be increased with the size in bytes of the read or write operation, by this way you can use it in subsequent calls to peek or poke functions.

 

   aRect[1] := PeekDWord(cRect,@nShift)

   aRect[2] := PeekDWord(cRect,@nShift)

   aRect[3] := PeekDWord(cRect,@nShift)

   aRect[4] := PeekDWord(cRect,@nShift)

end

return aRect

 

Peek functions have an alternate syntax to retrieve some members of the same type in only 1 call.

 

function aGetDesktopRect( lOk )

...

   aRect := PeekDWord(cRect,0,4) // returns an array of 4 LONG items