[DUG] Pointers help

[Stefan Mueller]

Ross,

 

“array of bytes” isn’t the same as a “pointer” (nor is the same as a static
array with a fixed length).  Dynamic arrays are a managed data structure in
Delphi that contain information such as length and a reference count (so
Delphi can manage memory and free them if no longer used). Converting data
from a memory-pointer to a dynamic array isn’t possible by typecasting
alone, you will need to copy the data as in your existing code – Indies
idGlobal.pas contains a helper function which does the same as your code:
function RawToBytes(const AValue; const ASize: Integer): TIdBytes;

 

 

Kind regards,



Stefan Müller,
R&D Manager

ORCL Toolbox Ltd. 
Auckland, New Zealand 


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From: delphi-bounces at listserver.123.net.nz
[mailto:delphi-bounces at listserver.123.net.nz] On Behalf Of Ross Levis
Sent: Sunday, 5 November 2017 2:19 p.m.
To: delphi at delphi.org.nz
Subject: [DUG] Pointers help

 

I’m writing data to an Indy IOHandler by moving the data from a
TMemoryStream.Memory to a TIDBytes (array of byte) before writing it as I
cannot find how to do it otherwise.

 

This works...

 

AudioMS: TMemoryStream;

Buffer: TIdBytes; // array of byte

MemPos: PByte;

....

MemPos := AudioMS.Memory;

Inc(MemPos,FromPos);

ToPos := Player.AudioMS.Position;

SetLength(Buffer,ToPos-FromPos);

Move(MemPos^,Buffer[0],Length(Buffer));

IOHandler.WriteDirect(Buffer);

FromPos := ToPos;

 

 

But there has to be a better way of writing direct from the AudioMS.Memory
and getting rid of the Move operation.

 

I’ve tried the following but produces pointer errors or access violations.

 

IOHandler.WriteDirect(TIdBytes(MemPos),ToPos-FromPos);

 

Also tried...

IOHandler.WriteDirect(TIdBytes(MemPos^),ToPos-FromPos);

 

There is a IOHandler.Write function that supports TStream but the memory
stream is being appended to in a separate thread so I can’t go changing the
Position I want to access the data from. 

 

 

How should it be done?

 

Cheers,

Ross.

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