Thread: Streambuf overloading with sputbackc

  1. #1
    Registered User
    Join Date
    May 2017

    Streambuf overloading with sputbackc

    I want to have a simple way to replace a istream or ostream in order to do on-line filtering of the content (for instance: add 1 to each character when reading, remove 1 when writing). It has to support operations like unget and putback

    I think the easiest way might be to overload streambuf

    I thought this would be something very easy, but it seems most of the code I'm doing results in error when code tries to do a unget

    Could someone show me how to subclass a streambuf to do online filtering (char by char) which I can then put in a istream or ostrea?

    Here is some code I'm using

    class FilteringBuf : public std::streambuf
        char readBuf_; // current char
        std::streambuf* pExternBuf_; // source buffer
        int_type underflow()
            if (gptr() == &readBuf_)
                return traits_type::to_int_type(readBuf_);
            int_type nextChar = pExternBuf_->sbumpc();
            if (nextChar == traits_type::eof())
                return traits_type::eof();
            readBuf_ = traits_type::to_char_type(nextChar);
            // replace character
            readBuf_ += 1;
            setg(&readBuf_, &readBuf_, &readBuf_ + 1);
            return traits_type::to_int_type(readBuf_);
        int_type overflow(int_type ch) {
            // replace character
            ch = ch - 1;
            return pExternBuf_->sputc(ch);
        int sync() {
            return pExternBuf_->pubsync();
            FilteringBuf(std::streambuf* pExternBuf)
                : pExternBuf_(pExternBuf)
            ~FilteringBuf() {
            void reset() {
                setg(0, 0, 0);
                setp(0, 0);

  2. #2
    Registered User
    Join Date
    Nov 2015
    I do not know, no, I'm not a code master.
    And provide all the code, I'm interested, and I'll compile your entire project, and I'll think and read.

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