[Lazarus] Copy buffer of PWord to TMemoryStream

[Sven Barth]

On 24.03.2013 19:57, Leonardo M. Ramé wrote:
> On 2013-03-24 19:46:09 +0100, Sven Barth wrote:
>> On 24.03.2013 19:30, Leonardo M. Ramé wrote:
>>> On 2013-03-24 19:21:49 +0100, Sven Barth wrote:
>>>> On 24.03.2013 19:19, Joao Morais wrote:
>>>>> 2013/3/24 Leonardo M. Ramé <l.rame at griensu.com>:
>>>>>> Hi, I'm copying a buffer of PWord to a TMemoryStream using this code:
>>>>>>
>>>>>> lTmpBuff := lBuffer;
>>>>>> I := 0;
>>>>>> while I < lBufSize do
>>>>>> begin
>>>>>>    lStream.Write(lTmpBuff^, SizeOf(PWord));
>>>>>>    inc(lTmpBuff, 1);
>>>>>>    inc(I, 1);
>>>>>
>>>>> What about:
>>>>>
>>>>>     inc(lTmpBuff, SizeOf(PWord));
>>>>>     inc(I, SizeOf(PWord));
>>>>
>>>> If lTmpBuff is declared as PWord then "Inc" already increases in
>>>> multiplies of "SizeOf(PWord)".
>>>> Regarding lBufSize it will be important to know whether the C code
>>>> returns the size in elements or in byte.
>>>>
>>>
>>> Heres the interface of the library:
[snip]
>> Now if your C function is written correctly, all three should give
>> you the same result.
>>
>
> Thanks Sven, I modified the C function as this:
>
> bufSize = interdata->getCount(); // <- returns number of pixels
> buffer = new Uint16[bufSize];
> memcpy((void *)buffer, interdata->getData(), interdata->getCount());
>
> Here's the getCount() documentation:
> http://support.dcmtk.org/docs/classDiPixel.html#15bbe5e57b15ea67bbc9541752ccccce
>
> Hence, my confusion is because I thought getCount was number of bytes,
> but it is number of pixels :)
>
> After changing the C function, now I can do this:
>
> lStream.Write(lTmpBuff^, SizeOf(PWord));
> inc(lTmpBuff);
> inc(I, 2); // it also works with inc(I, 1) but not using inc(I,
> sizeof(Word));
>

Now your lBufSize contains the number of pixels, so only Inc(I, 1) 
should be correct. And for copying all data at once you now need to use 
"lBufSize * SizeOf(Word)" instead. And the for-loop variant would look 
like this:

=== code begin ===

for i := 0 to lBufSize - 1 do
   lStream.Write(lBuffer[i], SizeOf(Word));
   // or
   lStream.WriteWord(lBuffer[i]);

=== code end ===

Regards,
Sven