How to write a file from cbytearray in chunks

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Hi all

i need to write a file from CByteArray, normally i do fast with:
WriteFile(hFile, btMemArray->GetData(), dwBytesToWrite, &dwBytesWritten, NULL);

but now i need a progressbar to follow the extraction, so i need to read chunks from cbytearray and write to file, but i cannot find a solution can you help me?

Thanks :)

What I have tried:

int nOffset = 0;

do
{
   bDone = WriteFile(hFile, btMemArray->GetData() + nOffset, 1, &dwBytesWritten, NULL);

   nOffset++;

} while (nOffset < btMemArray->GetSize());

<pre>

The my best was this at moment but i will need obviously bigger chunk than 1 help me to do this last step

Posted 2-May-20 1:44am

Drakesal

Updated 2-May-20 5:06am

v2

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Richard MacCutchan 2-May-20 8:41am

Why are you calling ZeroMemory when CopyMemory immediately overwrites the zeros?

It is not clear how you are co-ordinating between the reading (from where?) and the writing of the data, or how much actual data you will process.

[no name] 2-May-20 9:02am

There is no need of another buffer. CByteArray does give you the start address with GetData and the length of the array with GetSize so you can easely write chunk by chunk directly.

Drakesal 2-May-20 10:51am

int nOffset = 0;

do
{
bDone = WriteFile(hFile, btMemArray->GetData() + nOffset, 1, &dwBytesWritten, NULL);

nOffset++;

} while (nOffset < btMemArray->GetSize());

I have done this progress but how to use with higher chunk?

[no name] 2-May-20 11:16am

See Richard's answer which looks very good.

Drakesal 2-May-20 12:05pm

Thanks very much Richard you solved totally my problem, god bless you ;)

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Richard MacCutchan · Accepted Answer · 2020-05-02T05:07:00

Solution 2

It is only necessary to call GetSize and GetData once, before you start the loop. You can then use the returned values to walk the buffer writing your fixed size chunks. Something like:

C++

int chunksize = 1024; // or whatever size you want
DWORD dwBytesWritten;

int arraySize = btMemArray->GetSize();
byte* pByte = btMemArray->GetData();

while (arraySize > 0)
{
    if (arraySize < chunksize)
    {
        chunksize = arraySize; // any final short block
    }
    WriteFile(hFile, pByte, chunksize, &dwBytesWritten, NULL);
    // check for errors here
    pByte += chunksize;
    arraySize -= chunksize; // reduce the amount left write
}

Posted 2-May-20 5:07am

Richard MacCutchan

Updated 2-May-20 5:47am

v6

Comments

[no name] 2-May-20 11:14am

Looks fine, +5

Richard MacCutchan 2-May-20 11:17am

I had to rewrite it a few times as my brain got confused. :(

[no name] 2-May-20 11:19am

I had a solution 5 Min after you, but your code is much more readable than mine.
A small thing, here is a semicolon too much btMemArray->;GetData();

Richard MacCutchan 2-May-20 11:31am

Thanks, corrected. My old brain and the editor doing battle - you can see who won.

[no name] 2-May-20 11:36am

:-) same here a lot of time. Btw. another thing I see now: In case chunksize is bigger than the arraySize in the beginning one should limit it also at beginning of the loop.

Richard MacCutchan 2-May-20 11:46am

You are right of course. Is that better?

[no name] 2-May-20 11:50am

Perfect!