printf.h

/*
  Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

// Compared with std::stringstream, there are primary purpose of
// string::Printf:
//
// 1. Type-safe printing, with why and how explained in
//    http://www.drdobbs.com/stringprintf-a-typesafe-printf-family-fo/184401999.
//    Implementation includes
//
//    https://github.com/c42f/tinyformat
//    boost::format
//    std::stringstream
//
//    std::stringstream is not convenient enough in many cases.  For example:
//
//      std::cout << std::setprecision(2) << std::fixed << 1.23456 << "\n";
//
//    boost::format is the most convenient one.  We can have
//
//      std::cout << format("%2% %1%") % 36 % 77;
//
//    or
//
//      format fmter("%2% %1%");
//      fmter % 36; fmter % 77;
//      std::cout << fmter.c_str();
//
//    But the overloading of % might be overkilling and it would be
//    more efficient if it can write to std::cout directly.
//
//    tinyformat has an interface compatible with the C-printf style,
//    and it can writes to a stream or returns a std::string:
//
//      std::cout << tfm::printf(
//                  "%s, %s %d, %.2d:%.2d\n",
//                  weekday, month, day, hour, min);
//
//    or
//
//      tfm::format(std::cout,
//                  "%s, %s %d, %.2d:%.2d\n",
//                  weekday, month, day, hour, min);
//
// 2. High-performance -- most printed strings are not too long and
//    doens't need dynamic memory allocation.  Many StringPrintf
//    implementations doesn't enforce type-safe, but are
//    high-performance, including
//
//    https://developers.google.com/optimization/reference/base/stringprintf/
//    https://github.com/adobe/chromium/blob/master/base/stringprintf.h
//    https://github.com/google/protobuf/blob/master/src/google/protobuf/stubs/stringprintf.h
//
// According to
// https://github.com/c42f/tinyformat#compile-time-and-code-bloat,
// boost::format runs too slow and results in large executable binary
// files.  So here we port tinyformat.

#pragma once

#include <iostream>
#include <sstream>
#include "paddle/string/tinyformat/tinyformat.h"  // https://github.com/c42f/tinyformat

namespace paddle {
namespace string {

template <typename... Args>
void Fprintf(std::ostream& out, const char* fmt, const Args&... args) {
  tinyformat::vformat(out, fmt, tinyformat::makeFormatList(args...));
}

template <typename... Args>
std::string Sprintf(const char* fmt, const Args&... args) {
  std::ostringstream oss;
  Fprintf(oss, fmt, args...);
  return oss.str();
}

template <typename... Args>
void Printf(const char* fmt, const Args&... args) {
  Fprintf(std::cout, fmt, args...);
}

}  // namespace string
}  // namespace paddle