A question about using Low Level I/O API to read/write binary file

[Guest Bill David]

I use Low Level I/O API (_open) to create a binary file. Then I use

_chsize to set the size of this file (a big size). And then I _open

this file for reading (get fd1), and _open it for writing (get fd2)

and _write something to it. After that, I _read something from the

beginning with fd1, but find:

1.I have written 65535 bytes to the file; (with fd1)

2.But I can only read 126 bytes out with the 3rd parameter as 1024.

(with fd2)

Is it possible? How to avoid it?

 

Note:

1.Everything should have been done in a single thread.

2.I am writing an extension for another product, I must use fd

instead

of FILE* that's why I use Low Level I/O API instead of buffered FILE

I/

O.

3.the following is part of my log:

CStreamFileAccessor checkStatus, data length=65535. -

CStreamFileAccessor checkStatus, written bytes=65535. - --

>result

of write with fd2

CPlainFileAccessor updateStatusRecord, blockId=1,nBlocks=1. -

CStreamFileAccessor call ::read,

iHandle=3,uOffset=0,nBytes=1024. -

-->request for 1024 bytes

CConcreteFileAdaptor after reading, nCount=126. - --

[Guest Anthony [MVP]]

Re: A question about using Low Level I/O API to read/write binary file

 

I think this probably belongs in platformsdk newsgroup

 

"Bill David" <billdavidcn@gmail.com> wrote in message

news:a70c1a62-88d2-44eb-a9a8-b4eec7e49e41@p10g2000prf.googlegroups.com...

> I use Low Level I/O API (_open) to create a binary file. Then I use

> _chsize to set the size of this file (a big size). And then I _open

> this file for reading (get fd1), and _open it for writing (get fd2)

> and _write something to it. After that, I _read something from the

> beginning with fd1, but find:

> 1.I have written 65535 bytes to the file; (with fd1)

> 2.But I can only read 126 bytes out with the 3rd parameter as 1024.

> (with fd2)

> Is it possible? How to avoid it?

>

> Note:

> 1.Everything should have been done in a single thread.

> 2.I am writing an extension for another product, I must use fd

> instead

> of FILE* that's why I use Low Level I/O API instead of buffered FILE

> I/

> O.

> 3.the following is part of my log:

> CStreamFileAccessor checkStatus, data length=65535. -

> CStreamFileAccessor checkStatus, written bytes=65535. - --

>>result

> of write with fd2

> CPlainFileAccessor updateStatusRecord, blockId=1,nBlocks=1. -

> CStreamFileAccessor call ::read,

> iHandle=3,uOffset=0,nBytes=1024. -

> -->request for 1024 bytes

> CConcreteFileAdaptor after reading, nCount=126. - --