[boost] [iostreams] non buffered stream issues

Subject: [boost] [iostreams] non buffered stream issues
From: Christopher Lux (christopherlux_at_[hidden])
Date: 2008-09-18 07:55:02

Hi,
i wrote my own file device to get large file support on windows without 
the system caching the file.

now, when i use this device with boost::iostreams::stream or 
stream_buffer all read and write access is buffered (default 4096). i 
found the suggestion to create the stream or stream_buffer with a buffer 
size of 0, but then the access to the read or write function of the 
device are always for 1 byte. what can i do to get real unbuffered 
access to the device.

another problem. i use the device with the default buffer size of 4096. 
and access it like follows:

boost::iostreams::stream<mydevice> ifile;

char* buf = new char[3200];

for (int i = 0; i < 100; ++i) {
     ifile.seekg(32 * i, std::ios_base::beg);
     ifile.read(buf, 32);
}

now with the first read the buffer of 4096byte is filled up. then i seek 
32 byte into the file and the next read operation AGAIN reads from the 
device? why buffer when this case it not caught?

i am using boost 1.35.

regards
-chris
-- 
Christopher Lux |
                 | Bauhaus-Universität Weimar
                 | faculty of media - virtual reality systems group