chromium/third_party/abseil-cpp/absl/strings/internal/ostringstream.h

// Copyright 2017 The Abseil Authors.
//
// 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
//
//      https://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.

#ifndef ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
#define ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_

#include <cassert>
#include <ios>
#include <ostream>
#include <streambuf>
#include <string>
#include <utility>

#include "absl/base/config.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace strings_internal {

// The same as std::ostringstream but appends to a user-specified std::string,
// and is faster. It is ~70% faster to create, ~50% faster to write to, and
// completely free to extract the result std::string.
//
//   std::string s;
//   OStringStream strm(&s);
//   strm << 42 << ' ' << 3.14;  // appends to `s`
//
// The stream object doesn't have to be named. Starting from C++11 operator<<
// works with rvalues of std::ostream.
//
//   std::string s;
//   OStringStream(&s) << 42 << ' ' << 3.14;  // appends to `s`
//
// OStringStream is faster to create than std::ostringstream but it's still
// relatively slow. Avoid creating multiple streams where a single stream will
// do.
//
// Creates unnecessary instances of OStringStream: slow.
//
//   std::string s;
//   OStringStream(&s) << 42;
//   OStringStream(&s) << ' ';
//   OStringStream(&s) << 3.14;
//
// Creates a single instance of OStringStream and reuses it: fast.
//
//   std::string s;
//   OStringStream strm(&s);
//   strm << 42;
//   strm << ' ';
//   strm << 3.14;
//
// Note: flush() has no effect. No reason to call it.
class OStringStream final : public std::ostream { … };

}  // namespace strings_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_