How does this work? (StrPtr)

[Edwin Knoppert]

I discovered that String Ptr somehow maintains it's string length in the provided handle.
How can this be?
Where is it stored?
Should i make precautions because i make different uses of the same heapalloc.
I can't imagne that PB somewhere keeps a reference.

A copy of 2 heapallocs 'copies' this same length indicator!

#Compile Exe
#Include "win32api.inc"
 
Function PbMain
 
    Dim h1 As Long
    Dim h2 As Long
    Dim h3 As Long
    Dim T1 As String Ptr
    Dim T2 As String Ptr
    Dim T3 As String Ptr
 
    h1 = HeapAlloc( GetProcessHeap(), %HEAP_ZERO_MEMORY, 1000 )
    h2 = HeapAlloc( GetProcessHeap(), %HEAP_ZERO_MEMORY, 1000 )
    h3 = HeapAlloc( GetProcessHeap(), %HEAP_ZERO_MEMORY, 1000 )
 
    T1 = h1
 
    MsgBox "1> " & Str$( Len( @T1 ) )
 
 
    @T1 = Space$( 500 )
    MsgBox "2> " & Str$( Len( @T1 ) )
 
 
    T2 = h1
    MsgBox "3> " & Str$( Len( @T2 ) )
 
 
    MoveMemory h3, h1, 1000
    T3 = h3
    MsgBox "4> " & Str$( Len( @T3 ) )
 
 
    If h1 Then Call HeapFree( GetProcessHeap(), 0, ByVal h1 )
    If h2 Then Call HeapFree( GetProcessHeap(), 0, ByVal h2 )
    If h3 Then Call HeapFree( GetProcessHeap(), 0, ByVal h3 )
 
End Function

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[Semen Matusovski]

Edwin --
From PB/DLL help:

If you need to determine the current length of a dynamic string, there are two ways to do so.
The end of string is always followed by a nul, CHR$(0), so it is possible to scan the string for the first occurrence.
Of course, this will only work if there are no embedded nuls in the string data.

An alternative method is to read the 32-bit long integer which immediately precedes the start of the string data, as the current length is always stored there.

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