Re: Streaming to a device
fuzzyBuzz wrote:
I need to write a library for read/write access to a device.
[...]
My first thought was to derive my own class from one of the <iostream>
classes. istream and ostream seem like the natural candidates for input
and output classes respectively.
Almost. A stream consists of three parts:
- stream buffer
- locale
- flags and settings
Of those three, only the flags and settings are contained in the stream
itself, all others are plugins. Of those, the stream buffer is what you
actually want, because it is the one that does the actual input and output
of bytes.
Example: an fstream is just a class that derives from iostream and contains
an additional filebuf member. This member is plugged into the baseclass as
stream buffer. Otherwise, the fstream class itself is almost empty, all
functionality is contained in the baseclass code or the stream buffer code!
For you, that means that you create a class derived from streambuf, not from
istream or ostream. Note that there is no special stream buffer for input
or output, but stream buffers can signal at runtime that input or output
failed. If you search the web, you will find several examples. For output,
you only need to overload the overflow() function, for input you need two
functions IIRC (I forgot which those are).
If you can, try to get hold of Langer and Kreft's _C++ IOStreams and
Locales_, that book explains all those things and a lot more.
Uli
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