c++ - 可搜索输入过滤器定义

Question

使用 boost，我需要一个可搜索的输入过滤器，它将对从 ifstream 读取的字节进行操作。这是我目前拥有的:

struct my_filter : boost::iostreams::seekable_filter
{
    template<typename Source>
    int get(Source& src)
    {
        int byte = boost::iostreams::get(src);
        if(byte != EOF && byte != boost::iostreams::WOULD_BLOCK)
        {
            // Do something with byte
        }
        return byte;
    }

    template<typename Sink>
    bool put(Sink&, char)
    {
        // No need to actually implement put because this filter is only used with ifstream
        return true;
    }

    template<typename T>
    std::streampos seek(T& t, boost::iostreams::stream_offset off, std::ios_base::seekdir way, std::ios_base::openmode which = std::ios_base::in | std::ios_base::out)
    {
        return boost::iostreams::seek(t, off, way, which);
    }
};

它有效，但我想摆脱无用的 put 方法。这里的 boost 文档 http://www.boost.org/doc/libs/1_60_0/libs/iostreams/doc/concepts/filter.html说有一个 Filter 的 InputSeekableFilter 改进，但我似乎无法理解如何使用它(没有我可以使用的 input_seekable_filter_tag 或 input_seekable_filter 结构)。

Answer 1

llonesmiz 在 boost-users 上的回答:

"boost::iostreams::seekable_filter" seems to just be a typedef for "boost::iostreams::filter<boost::iostreams::seekable>". I don't know for sure, but I think it would make sense that deriving your "struct my_filter" from "boost::iostreams::filter<boost::iostreams::input_seekable>" would accomplish what you want.