Re: delimiter for istringstream
Denise Kleingeist wrote:
Z.L. wrote:
P.S. I am very curious about "filtering streambuf" scheme you
mentioned. Could you explain it for me? Thank you very much.
I'm obviously not James but I still can describe filtering stream
buffers:
basically, the idea is to have a stream buffer which just delegates the
actual I/O operations to an underlying stream buffer after doing some
processing on its own. For example, a filtering stream buffer could
read a buffer full of data from an underlying stream buffer,
std::transform() all colons into spaces and supply these in its own
buffer. All this processing would be done in the filtering stream
buffer's
underflow() method. This would look something like this:
class filterbuf: public std::streambuf {
public:
filterbuf(std::streambuf* stream): myStream(stream) {}
private:
int_type underflow() {
if (this->gptr() == this->egptr()) {
std::streamsize size = this->myStream->sgetn(this->myBuffer,
1024);
this->setg(this->myBuffer, this->myBuffer,
std::transform(this->myBuffer + 0,
this->myBuffer + size, ':', ' '));
Now that's clever, hiding the transformation in an argument to
setg, so that the reader won't see it unless he carefully
analyses each step in detail. I'll have to remember it next
time I'm trying to obfuscate code.
}
return this->gptr() != this->egptr()?
traits_type::to_int_type(this->gptr(): traits_type::eof();
}
std::streambuf* myStream;
char myBuffer[1024];
};
In general, unless there is a definite reason for doing
otherwise, I tend to avoid bufferisation in a filtering
streambuf. It makes synchronization between the filtering
streambuf and the filtered streambuf more complicated. (This is
typically not a problem if you are reading the entire stream
through the filtering streambuf, but I often insert then just
for a part of the stream.) And of course, buffering is also
more complicated if the transformation is not one to one, which
is often the case (although not the case here).
--
James Kanze (GABI Software) email:james.kanze@gmail.com
Conseils en informatique orient?e objet/
Beratung in objektorientierter Datenverarbeitung
9 place S?mard, 78210 St.-Cyr-l'?cole, France, +33 (0)1 30 23 00 34
--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]