iostreams::tee_filter is for output only

[alexis_wilke]

I faught the C++ compiler for a little while before I realized that the iostreams::tee_filter was written as an output filter only. I needed it to work for an input chain and I do not see why there is such a limitation.

My idea is to catch a copy of the data somewhere in the chain before it gets transformed further. Whether it is input our output it should work, right? (at least in theory...)

Anyone has input in that regard?

Thank you,
Alexis Wilke

[alexis_wilke]

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I propose the following additional function and adding multichar_input_filter_tag to the category. My software seems to work just fine with this addition.


    template<typename Source>
    std::streamsize read(Source& src, char_type* s, std::streamsize n)
    {
        int   c;
        char_type* first = s;
        char_type* last  = s + n;
        while ( first != last &&
                (c = boost::iostreams::get(src)) != EOF &&
                 c != WOULD_BLOCK )
        {
            *first++ = c;
        }
        std::streamsize result = static_cast<std::streamsize>(first - s);
        if(result == 0)
        {
           return c;
        }
        std::streamsize result2 = iostreams::write(this->component(), s, result);
        (void) result2; // Suppress 'unused variable' warning.
        assert(result == result2);
        return result;
    }

[Jonathan Turkanis]

When I wrote tee, I couldn't think of a way to apply the concept to an input stream, but your idea looks pretty good. I will consider it for 1.36.

[Jonathan Turkanis]

(In [45752]) made tee work with input streams (fixes #791)