spdlog/include/spdlog/fmt/bundled/ostream.h

// Formatting library for C++ - std::ostream support
//
// Copyright (c) 2012 - 2016, Victor Zverovich
// All rights reserved.
//
// For the license information refer to format.h.

#ifndef FMT_OSTREAM_H_
#define FMT_OSTREAM_H_

#include "format.h"
#include <ostream>

FMT_BEGIN_NAMESPACE
namespace internal {

template<class Char>
class formatbuf : public std::basic_streambuf<Char>
{
private:
    typedef typename std::basic_streambuf<Char>::int_type int_type;
    typedef typename std::basic_streambuf<Char>::traits_type traits_type;

    basic_buffer<Char> &buffer_;

public:
    formatbuf(basic_buffer<Char> &buffer)
        : buffer_(buffer)
    {
    }

protected:
    // The put-area is actually always empty. This makes the implementation
    // simpler and has the advantage that the streambuf and the buffer are always
    // in sync and sputc never writes into uninitialized memory. The obvious
    // disadvantage is that each call to sputc always results in a (virtual) call
    // to overflow. There is no disadvantage here for sputn since this always
    // results in a call to xsputn.

    int_type overflow(int_type ch = traits_type::eof()) FMT_OVERRIDE
    {
        if (!traits_type::eq_int_type(ch, traits_type::eof()))
            buffer_.push_back(static_cast<Char>(ch));
        return ch;
    }

    std::streamsize xsputn(const Char *s, std::streamsize count) FMT_OVERRIDE
    {
        buffer_.append(s, s + count);
        return count;
    }
};

template<typename Char>
struct test_stream : std::basic_ostream<Char>
{
private:
    struct null;
    // Hide all operator<< from std::basic_ostream<Char>.
    void operator<<(null);
};

// Checks if T has a user-defined operator<< (e.g. not a member of
// std::ostream).
template<typename T, typename Char>
class is_streamable
{
private:
    template<typename U>
    static decltype(internal::declval<test_stream<Char> &>() << internal::declval<U>(), std::true_type()) test(int);

    template<typename>
    static std::false_type test(...);

    typedef decltype(test<T>(0)) result;

public:
    // std::string operator<< is not considered user-defined because we handle
    // strings
    // specially.
    static const bool value = result::value && !std::is_same<T, std::string>::value;
};

// Disable conversion to int if T has an overloaded operator<< which is a free
// function (not a member of std::ostream).
template<typename T, typename Char>
class convert_to_int<T, Char, true>
{
public:
    static const bool value = convert_to_int<T, Char, false>::value && !is_streamable<T, Char>::value;
};

// Write the content of buf to os.
template<typename Char>
void write(std::basic_ostream<Char> &os, basic_buffer<Char> &buf)
{
    const Char *data = buf.data();
    typedef std::make_unsigned<std::streamsize>::type UnsignedStreamSize;
    UnsignedStreamSize size = buf.size();
    UnsignedStreamSize max_size = internal::to_unsigned((std::numeric_limits<std::streamsize>::max)());
    do
    {
        UnsignedStreamSize n = size <= max_size ? size : max_size;
        os.write(data, static_cast<std::streamsize>(n));
        data += n;
        size -= n;
    } while (size != 0);
}

template<typename Char, typename T>
void format_value(basic_buffer<Char> &buffer, const T &value)
{
    internal::formatbuf<Char> format_buf(buffer);
    std::basic_ostream<Char> output(&format_buf);
    output.exceptions(std::ios_base::failbit | std::ios_base::badbit);
    output << value;
    buffer.resize(buffer.size());
}

// Disable builtin formatting of enums and use operator<< instead.
template<typename T>
struct format_enum<T, typename std::enable_if<std::is_enum<T>::value>::type> : std::false_type
{
};
} // namespace internal

// Formats an object of type T that has an overloaded ostream operator<<.
template<typename T, typename Char>
struct formatter<T, Char, typename std::enable_if<internal::is_streamable<T, Char>::value>::type> : formatter<basic_string_view<Char>, Char>
{

    template<typename Context>
    auto format(const T &value, Context &ctx) -> decltype(ctx.out())
    {
        basic_memory_buffer<Char> buffer;
        internal::format_value(buffer, value);
        basic_string_view<Char> str(buffer.data(), buffer.size());
        formatter<basic_string_view<Char>, Char>::format(str, ctx);
        return ctx.out();
    }
};

template<typename Char>
inline void vprint(
    std::basic_ostream<Char> &os, basic_string_view<Char> format_str, basic_format_args<typename buffer_context<Char>::type> args)
{
    basic_memory_buffer<Char> buffer;
    vformat_to(buffer, format_str, args);
    internal::write(os, buffer);
}
/**
  \rst
  Prints formatted data to the stream *os*.

  **Example**::

    fmt::print(cerr, "Don't {}!", "panic");
  \endrst
 */
template<typename... Args>
inline void print(std::ostream &os, string_view format_str, const Args &... args)
{
    vprint<char>(os, format_str, make_format_args<format_context>(args...));
}

template<typename... Args>
inline void print(std::wostream &os, wstring_view format_str, const Args &... args)
{
    vprint<wchar_t>(os, format_str, make_format_args<wformat_context>(args...));
}
FMT_END_NAMESPACE

#endif // FMT_OSTREAM_H_