NewLC - Please help, with buffers and/or arrays. - Comments

Re: Please help, with buffers and/or arrays.

Sikkimes — Tue, 27 May 2008 10:05:49 +0200

Perfect man,...
Instead of

iAudioBuffer.CreateL(16*4096);
iAudioBuffer.CreateMaxL(16*4096);

Do the work
Alternatively,

iAudioBuffer.CreateL(16*4096);
iAudioBuffer.SetMax();

Should work (I didnt tested it yet).

Append of course also works, but only if you add the buffers in order, and I thought a requirement was that they could come out-of-order.

Yep, trying to solve my problem, I create a method to sort them, losing some time, but doing it right...

Now I have more "tools" to do the reconstruction... I'll do it all over again, and in a few (7 ) days I'll let you know how did it go.

PD: For other people reading this thread this link may help a lot http://descriptors.blogspot.com/2005/06/33-can-you-give-example-of-how-to-use.html

Re: Please help, with buffers and/or arrays.

Sikkimes — Tue, 27 May 2008 09:50:02 +0200

We were posting at the same time, LOL.

Thanks for the explanation, I got it perfectly... I just wanted to use my -already created- structure to store my buffers, because when I receive packets I stored them in an array, and the reconstruction is made after in other method that I thought that could use the same array.
Graphically, it would be like this:

iAudioBuffer[0] = XXXXXXXXXX // buffer of 10 samples received OK
iAudioBuffer[1] = XXXXXXXXXX // buffer of 10 samples received OK
iAudioBuffer[2] = __________ // buffer lost <- this one I wanted to be able to reconstruct it sample by sample.
iAudioBuffer[3] = XXXXXXXXXX // buffer of 10 samples received OK

But its ok now, as my last post say, the method do what I wanted (although it sounds really bad )
Thanks. Bye.

Re: Please help, with buffers and/or arrays.

alh — Tue, 27 May 2008 09:47:39 +0200

Ah.. I think I know what the problem is now.

When you "Create" the buffer, you get a buffer with the maxlength of what you specify.
but Length is still set to 0, even though the memory for the whole array is allocated.
So before you can use = you have to do do:

iAudioBuffer.SetMax();

The out-of-bounds check on [] is on the Length and not on the MaxLength....

Append ofcourse also works, but only if you add the buffers in order, and I thought a requirement was that they could come out-of-order.

Append is also a bit slower since each assignment also has to update the length of the descriptor.

Re: Please help, with buffers and/or arrays.

Sikkimes — Tue, 27 May 2008 09:24:25 +0200

Ive already "found" (just by following alh indications) a solution, replacing the assignment ( = ) by Append().

RBuf8 iAudioBuffer; //.h
iAudioBuffer.CreateL(4096);
for(TInt i = 0; i < 4096; i++)
        iAudioBuffer.Append(aBuffer[i]);

because:

iAudioBuffer[i] = aBuffer[i]; // crashes

It doesnt sound like I expected, but at least do what I wanted to do
Thank you so much.

PD: Definitely I'll replace my TBufs with RBufs,... to create objects dynamically, makes my life easier

Re: Please help, with buffers and/or arrays.

alh — Tue, 27 May 2008 08:53:00 +0200

I think the problem is that this:

iAudioBuffer[0][startindex + i] = aBuffer[i]; // here it crashes.

should be:

iAudioBuffer[0][i] = aBuffer[i]; // here it crashes.

in your case.

My example used one single flat buffer, a single array, to store all audiodata.
Like this, here is place for 10 audiobuffers of 4096 bytes each:

__________

I called each of the logical buffers within the buffer for "subbuffers"
Then I used "startindex" to jump into the buffer, to write a part of it, lets say I want to write the 3rd audiobuffer.
I used startindex to step into it and after writing my buffer would look like
__X_______

Then I write the 5th buffer too and my buffer would look like

__X_X_____

Then write the 4th buffer and it would look like

__XXX_____

etc...

In your example code on the other hand, you do not use a flat buffer, you are using a 2-dimensional buffer, or as its also called "and array of arrays"

which could be diagrammed like this:

_
_
_
_
_
_

Then you use the first parantesis to select which "sub buffer", and you must use 0-based index to index into that sub-buffer.

I prefer the flat buffer approach, feels like I have more control, and I don't have to keep track of two indexes when using it.
And easier when scanning through all samples, since they all are guaranteed to be just after the previous sample in memory.

Re: Please help, with buffers and/or arrays.

Sikkimes — Mon, 26 May 2008 23:44:27 +0200

Mmmmm... Im a bit confused.
I can select what subbuffer to use by the first [], what I cant do is to write some bytes inside that buffer.

Let try in other words... I have an array of 16 TBuf8 objects, and I can access to them with iAudioBuffer[0], iAudioBuffer[1], ... iAudioBuffer[15], right?
Then what I need is to write the first, say, 5 bytes (==subbufers?) of one of this objects.
I thought that it has to be something like this:

( (iAudioBuffer[2]) [startindex] ) = myBlah;
(   (the Object)     theOffset   ) = myBlah;

But as I say it didnt work (I use parenthesis to prioritize)

Could you explain me how to do that?
Thanks a lot for ur time.

Re: Please help, with buffers and/or arrays.

alh — Mon, 26 May 2008 14:33:08 +0200

If you use a 2d-buffer, you don't have to offset with the "startindex", then you select what subbuffer to use by the first []

My example used a simple 1dimensional buffer, and then you need the "startindex" offset to jump to the next "subbuffer" within the buffer.

Similar to how you step between scanlines when accessing raw images...

Re: Please help, with buffers and/or arrays.

Sikkimes — Mon, 26 May 2008 09:06:42 +0200

Thanks to all of you guys.
The info provided by you give me good indications, and also helped me to understand more about this language.

But I have another problem/question : I have an array of buffers (still working with TBuf8 to make sure the functionality is working, once functionality is ok I'll move all my buffers to Rbuf8 I promess ) and I want to do the assignment suggested by alh, so how can I do that?

I supposed that

TBuf8<4096> iAudioBuffer[16]; // the array in my .h
iAudioBuffer[0-15][startindex + i] = aBuffer[i]; // here it crashes.

will do it, but it crashes with User -21 panic, telling me that some index is out of bounds.
[startindex + i] is 0 when it crashes, and the cause its not the arithmetic operation in the index of the array, because [0] (as a number) fails as well.

Im "completely" sure that aBuffer[i] has info and its not the cause of the problem (I write to a console its value and aBuffer[0] is 0).
I also know that iAudioBuffer[some sample between 1 to 16] has no data, because it hasn't been written by any method or function.
I thought that RBuf8 and TBuf8 could be distinct, but in this case, both has TUint8& operator[](TInt anIndex); inherited from TDes8.

Please help me...
Thanks once again

Re: Please help, with buffers and/or arrays.

Andreas — Wed, 21 May 2008 10:14:21 +0200

It's better to use RBuf8 or HBufC8 as alh suggested, and allocate your buffers dynamically. You can also use TDes::Insert to insert data in between existing data.

Re: Please help, with buffers and/or arrays.

jupitar — Tue, 20 May 2008 19:34:10 +0200

You can try increasing your stacksize by a significant amount using EPOCSTACKSIZE directive in your mmp file too.

Re: Please help, with buffers and/or arrays.

alh — Tue, 20 May 2008 11:19:52 +0200

You can write at any position in a TBuf, not only at the end.
just use operator[] to index into it.

You shouldn't use TBuf:s though for this, a better idea is RBufs, that always keep its storage on the heap.
TBuf:s this big, if declared as automatic stack variables will bust your stack very quickly.

RBuf8 iAudioBuffer; //a member in some class somewhere
TBool iHasContent[16]; //flag field would be more efficient, but bools are easy....

[...]
iAudioBuffer.CreateL(16*4096); // space for 16 samples;

[...]
void CMyClass::AddSample(TInt aSampleNo, const TDesC8& aBuffer) {
   TInt startindex = aSampleNo*4096;
   for(TInt i = 0; i < 4096; i++) {
     iAudioBuffer[startindex + i] = aBuffer[i];
  }
  iHasContent[aSampleNo] = ETrue;
}

(Its possible to make a little bit more efficient using Mem::Copy instead of a for-loop)

Please help, with buffers and/or arrays.

Sikkimes — Tue, 20 May 2008 11:02:59 +0200

Hi everybody,

Im trying to measure some technics about audio reconstruction in symbian, and to do that Im sending 4 mixed packets of 4 samples of audio to a receiver to do the reconstruction. I mean, the sequence is:
- to record 16 samples of audio
- to add a header to each one to indicate his original position
- to pack groups of 4 samples of audio
- and send it to receiver