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 <ostream>
#include "format.h"

FMT_BEGIN_NAMESPACE
namespace internal {

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

  buffer<Char>& buffer_;

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

 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((void)(std::declval<test_stream<Char>&>()
                         << std::declval<U>()),
                  std::true_type())
  test(int);

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

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

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

// Write the content of buf to os.
template <typename Char>
void write(std::basic_ostream<Char>& os, buffer<Char>& buf) {
  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((std::numeric_limits<std::streamsize>::max)());
  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) {
  formatbuf<Char> format_buf(buf);
  std::basic_ostream<Char> output(&format_buf);
  output.exceptions(std::ios_base::failbit | std::ios_base::badbit);
  output << value;
  buf.resize(buf.size());
}

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

template <typename Char>
void vprint(std::basic_ostream<Char>& os, basic_string_view<Char> format_str,
            basic_format_args<buffer_context<Char>> args) {
  basic_memory_buffer<Char> buffer;
  internal::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 S, typename... Args,
          typename Char = enable_if_t<internal::is_string<S>::value, char_t<S>>>
void print(std::basic_ostream<Char>& os, const S& format_str, Args&&... args) {
  vprint(os, to_string_view(format_str),
         {internal::make_args_checked<Args...>(format_str, args...)});
}
FMT_END_NAMESPACE

#endif  // FMT_OSTREAM_H_