// 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 <ostream> #include <streambuf> #include <string> #include "absl/base/port.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 : 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 ABSL_NAMESPACE_END } // namespace absl #endif // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_