spdlog/include/c11log/details/fast_oss.h

#pragma once

// A faster-than-ostringstream class
// uses stack_buf as the underlying buffer (upto 192 bytes before using the heap)

#include <ostream>
#include <iomanip>
#include "stack_buf.h"

namespace c11log
{
namespace details
{

class stack_devicebuf :public std::streambuf
{
public:
    static const unsigned short stack_size = 192;
    using stackbuf_t = stack_buf<stack_size>;

    stack_devicebuf() = default;
    ~stack_devicebuf() = default;
    stack_devicebuf& operator=(const stack_devicebuf&) = delete;

    stack_devicebuf(const stack_devicebuf& other) :std::basic_streambuf<char>(), _stackbuf(other._stackbuf)
    {}

    stack_devicebuf(stack_devicebuf&& other):
        std::basic_streambuf<char>(),
        _stackbuf(std::move(other._stackbuf))
    {
        other.clear();
    }

    stackbuf_t::bufpair_t buf() const
    {
        return _stackbuf.get();
    }

    std::size_t size() const
    {
        return _stackbuf.size();
    }

    void clear()
    {
        _stackbuf.clear();
    }

protected:
    // copy the give buffer into the accumulated fast buffer
    std::streamsize xsputn(const char_type* s, std::streamsize count) override
    {
        _stackbuf.append(s, static_cast<unsigned int>(count));
        return count;
    }

    int_type overflow(int_type ch) override
    {
        if (traits_type::not_eof(ch))
        {
            char c = traits_type::to_char_type(ch);
            xsputn(&c, 1);
        }
        return ch;
    }
private:
    stackbuf_t _stackbuf;
};


class fast_oss :public std::ostream
{
public:
    fast_oss() :std::ostream(&_dev) {}
    ~fast_oss() = default;

    fast_oss& operator=(const fast_oss& other) = delete;
    fast_oss& operator=(const fast_oss&& other) = delete;

    fast_oss(const fast_oss& other) :std::basic_ios<char>(), std::ostream(&_dev), _dev(other._dev)
    {}

    fast_oss(fast_oss&& other) :std::basic_ios<char>(), std::ostream(&_dev), _dev(std::move(other._dev))
    {
        other.clear();
    }

    std::string str()
    {
        auto buf = _dev.buf();
        return std::string(buf.first, buf.second);
    }


    std::size_t size() const
    {
        return _dev.size();
    }

    void clear()
    {
        _dev.clear();
    }

private:
    stack_devicebuf _dev;
};
}
}