fmt/include/fmt/ostream.h

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

#ifndef FMT_OSTREAM_H_
#define FMT_OSTREAM_H_

#include <fstream>
#include <ostream>

#include "format.h"

FMT_BEGIN_NAMESPACE

template <typename OutputIt, typename Char> class basic_printf_context;

namespace detail {

// Checks if T has a user-defined operator<<.
template <typename T, typename Char, typename Enable = void>
class is_streamable {
 private:
  template <typename U>
  static auto test(int)
      -> bool_constant<sizeof(std::declval<std::basic_ostream<Char>&>()
                              << std::declval<U>()) != 0>;

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

  using result = decltype(test<T>(0));

 public:
  is_streamable() = default;

  static const bool value = result::value;
};

// Formatting of built-in types and arrays is intentionally disabled because
// it's handled by standard (non-ostream) formatters.
template <typename T, typename Char>
struct is_streamable<
    T, Char,
    enable_if_t<
        std::is_arithmetic<T>::value || std::is_array<T>::value ||
        std::is_pointer<T>::value || std::is_same<T, char8_type>::value ||
        std::is_convertible<T, fmt::basic_string_view<Char>>::value ||
        std::is_same<T, std_string_view<Char>>::value ||
        (std::is_convertible<T, int>::value && !std::is_enum<T>::value)>>
    : std::false_type {};

template <typename Char> FILE* get_file(std::basic_filebuf<Char>&) {
  return nullptr;
}

struct dummy_filebuf {
  FILE* _Myfile;
};
template <typename T, typename U = int> struct ms_filebuf {
  using type = dummy_filebuf;
};
template <typename T> struct ms_filebuf<T, decltype(T::_Myfile, 0)> {
  using type = T;
};
using filebuf_type = ms_filebuf<std::filebuf>::type;

FILE* get_file(filebuf_type& buf);

// Generate a unique explicit instantion in every translation unit using a tag
// type in an anonymous namespace.
namespace {
struct filebuf_access_tag {};
}  // namespace
template <typename Tag, typename FileMemberPtr, FileMemberPtr file>
class filebuf_access {
  friend FILE* get_file(filebuf_type& buf) { return buf.*file; }
};
template class filebuf_access<filebuf_access_tag,
                              decltype(&filebuf_type::_Myfile),
                              &filebuf_type::_Myfile>;

inline bool write(std::filebuf& buf, fmt::string_view data) {
  FILE* f = get_file(buf);
  if (!f) return false;
  print(f, data);
  return true;
}
inline bool write(std::wfilebuf&, fmt::basic_string_view<wchar_t>) {
  return false;
}

// Write the content of buf to os.
// It is a separate function rather than a part of vprint to simplify testing.
template <typename Char>
void write_buffer(std::basic_ostream<Char>& os, buffer<Char>& buf) {
  if (const_check(FMT_MSC_VERSION)) {
    auto filebuf = dynamic_cast<std::basic_filebuf<Char>*>(os.rdbuf());
    if (filebuf && write(*filebuf, {buf.data(), buf.size()})) return;
  }
  const Char* buf_data = buf.data();
  using unsigned_streamsize = std::make_unsigned<std::streamsize>::type;
  unsigned_streamsize size = buf.size();
  unsigned_streamsize max_size = to_unsigned(max_value<std::streamsize>());
  do {
    unsigned_streamsize n = size <= max_size ? size : max_size;
    os.write(buf_data, static_cast<std::streamsize>(n));
    buf_data += n;
    size -= n;
  } while (size != 0);
}

template <typename Char, typename T>
void format_value(buffer<Char>& buf, const T& value,
                  locale_ref loc = locale_ref()) {
  auto&& format_buf = formatbuf<std::basic_streambuf<Char>>(buf);
  auto&& output = std::basic_ostream<Char>(&format_buf);
#if !defined(FMT_STATIC_THOUSANDS_SEPARATOR)
  if (loc) output.imbue(loc.get<std::locale>());
#endif
  output << value;
  output.exceptions(std::ios_base::failbit | std::ios_base::badbit);
}
}  // namespace detail

// Formats an object of type T that has an overloaded ostream operator<<.
template <typename Char>
struct basic_ostream_formatter : formatter<basic_string_view<Char>, Char> {
  template <typename T, typename OutputIt>
  auto format(const T& value, basic_format_context<OutputIt, Char>& ctx) const
      -> OutputIt {
    auto buffer = basic_memory_buffer<Char>();
    format_value(buffer, value, ctx.locale());
    return formatter<basic_string_view<Char>, Char>::format(
        {buffer.data(), buffer.size()}, ctx);
  }
};

using ostream_formatter = basic_ostream_formatter<char>;

namespace detail {

// Formats an object of type T that has an overloaded ostream operator<<.
template <typename T, typename Char>
struct fallback_formatter<T, Char, enable_if_t<is_streamable<T, Char>::value>>
    : basic_ostream_formatter<Char> {
  using basic_ostream_formatter<Char>::format;
};

}  // namespace detail

FMT_MODULE_EXPORT
template <typename Char>
void vprint(std::basic_ostream<Char>& os,
            basic_string_view<type_identity_t<Char>> format_str,
            basic_format_args<buffer_context<type_identity_t<Char>>> args) {
  auto buffer = basic_memory_buffer<Char>();
  detail::vformat_to(buffer, format_str, args);
  detail::write_buffer(os, buffer);
}

/**
  \rst
  Prints formatted data to the stream *os*.

  **Example**::

    fmt::print(cerr, "Don't {}!", "panic");
  \endrst
 */
FMT_MODULE_EXPORT
template <typename... T>
void print(std::ostream& os, format_string<T...> fmt, T&&... args) {
  vprint(os, fmt, fmt::make_format_args(args...));
}

FMT_MODULE_EXPORT
template <typename... Args>
void print(std::wostream& os,
           basic_format_string<wchar_t, type_identity_t<Args>...> fmt,
           Args&&... args) {
  vprint(os, fmt, fmt::make_format_args<buffer_context<wchar_t>>(args...));
}

FMT_END_NAMESPACE

#endif  // FMT_OSTREAM_H_