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// 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
//
// 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.
#ifndef ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
#define ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
#include <cassert>
#include <ostream>
#include <streambuf>
#include <string>
#include "absl/base/port.h"
namespace absl {
inline namespace lts_2018_06_20 {
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 : private std::basic_streambuf<char>, public std::ostream {
public:
// The argument can be null, in which case you'll need to call str(p) with a
// non-null argument before you can write to the stream.
//
// The destructor of OStringStream doesn't use the std::string. It's OK to destroy
// the std::string before the stream.
explicit OStringStream(std::string* s) : std::ostream(this), s_(s) {}
std::string* str() { return s_; }
const std::string* str() const { return s_; }
void str(std::string* s) { s_ = s; }
private:
using Buf = std::basic_streambuf<char>;
Buf::int_type overflow(int c) override;
std::streamsize xsputn(const char* s, std::streamsize n) override;
std::string* s_;
};
} // namespace strings_internal
} // inline namespace lts_2018_06_20
} // namespace absl
#endif // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
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