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From: Larry on 15 Jan 2010 10:17
WAVEHDR allocationg several buffers

Hi,

I'm dealing with WAVEHDR from the waveForm API. I'd like to know which of
the following is the best approach to set up some buffers:


1)
// Define WAVEHDR Structure:

WAVEHDR *buff = new WAVEHDR[num_buffers];

for (int i = 0; i<num_buffers; i++)
{
ZeroMemory(&buff[i], sizeof(buff[i]));
buff[i].lpData = (LPSTR) malloc(system_buf_len);
buff[i].dwBufferLength = system_buf_len;
buff[i].dwBytesRecorded = 0;
buff[i].dwUser = 0;
buff[i].dwFlags = 0;
buff[i].dwLoops = 0;

if(waveInPrepareHeader(hwi, &buff[i], sizeof(WAVEHDR)) != MMSYSERR_NOERROR)
printf("waveInPrepareHedare: ERROR!\n"); // return -1;

if(waveInAddBuffer(hwi, &buff[i], sizeof(WAVEHDR)) != MMSYSERR_NOERROR)
printf("waveInAddBuffer: ERROR!\n"); // return -1;
}


2)
// Define WAVEHDR Structure:

WAVEHDR **buff = new WAVEHDR*[num_buffers];

for (int i = 0; i<num_buffers; i++)
{
buff[i] = new WAVEHDR;
ZeroMemory(buff[i],sizeof(WAVEHDR));
buff[i]->lpData = new char[system_buf_len;]
buff[i]->dwBufferLength = system_buf_len;
buff[i]->dwBytesRecorded = 0;
buff[i]->dwUser = 0;
buff[i]->dwFlags = 0;
buff[i]->dwLoops = 0;

if(waveInPrepareHeader(hwi, buff[i], sizeof(WAVEHDR)) != MMSYSERR_NOERROR)
printf("waveInPrepareHedare: ERROR!\n"); // return -1;

if(waveInAddBuffer(hwi, buff[i], sizeof(WAVEHDR)) != MMSYSERR_NOERROR)
printf("waveInAddBuffer: ERROR!\n"); // return -1;
}

thanks

NB: both of them seems to be working fine!

From: Giovanni Dicanio on 15 Jan 2010 12:29
"Larry" <dontmewithme(a)got.it> ha scritto nel messaggio
news:4b508721$0$823$4fafbaef(a)reader5.news.tin.it...

> I'd like to know which of the following is the best approach to set up
> some buffers:

> 1)
> // Define WAVEHDR Structure:
>
> WAVEHDR *buff = new WAVEHDR[num_buffers];

> 2)
> // Define WAVEHDR Structure:
>
> WAVEHDR **buff = new WAVEHDR*[num_buffers];
>
> for (int i = 0; i<num_buffers; i++)
> {
> buff[i] = new WAVEHDR;

I'm not sure, but I think that option #1 would give you better locality,
because the WAVEHDR instances are allocated contiguously (instead, in
version #2, you allocate the pointers WAVEHDR* contiguously, but the
instances of WAVEHDR can be scattered in the heap).

Giovanni


From: Tim Roberts on 16 Jan 2010 21:11
"Larry" <dontmewithme(a)got.it> wrote:
>
>WAVEHDR allocationg several buffers
>
> I'm dealing with WAVEHDR from the waveForm API. I'd like to know which of
>the following is the best approach to set up some buffers:

The "best" choice depends on your definition of the word "best".

>1)
>WAVEHDR *buff = new WAVEHDR[num_buffers];
>
>for (int i = 0; i<num_buffers; i++)
>{
> ZeroMemory(&buff[i], sizeof(buff[i]));
> buff[i].lpData = (LPSTR) malloc(system_buf_len);
>2)
>WAVEHDR **buff = new WAVEHDR*[num_buffers];
>
>for (int i = 0; i<num_buffers; i++)
>{
> buff[i] = new WAVEHDR;
> ZeroMemory(buff[i],sizeof(WAVEHDR));
> buff[i]->lpData = new char[system_buf_len;]

I see no justification for allocating the WAVEHDRs individually. On the
other hand, you could let the system help you by doing:

std::vector<WAVEHDR> buff;
buff.resize(num_buffers);

As for the individual buffers, that's really up to you. At the lowest
level, "malloc" and "new" both map to the same low-level APIs. In a C++
program, I usually prefer "new" to "malloc".
--
Tim Roberts, timr(a)probo.com
Providenza & Boekelheide, Inc.
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