Abseil Common Libraries (C++) (grcp 依赖)
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97 lines
2.9 KiB
97 lines
2.9 KiB
// Copyright 2017 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// http://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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#ifndef ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_ |
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#define ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_ |
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#include <cassert> |
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#include <ostream> |
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#include <streambuf> |
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#include <string> |
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#include "absl/base/port.h" |
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namespace absl { |
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namespace strings_internal { |
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// The same as std::ostringstream but appends to a user-specified std::string, |
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// and is faster. It is ~70% faster to create, ~50% faster to write to, and |
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// completely free to extract the result std::string. |
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// |
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// std::string s; |
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// OStringStream strm(&s); |
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// strm << 42 << ' ' << 3.14; // appends to `s` |
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// |
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// The stream object doesn't have to be named. Starting from C++11 operator<< |
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// works with rvalues of std::ostream. |
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// |
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// std::string s; |
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// OStringStream(&s) << 42 << ' ' << 3.14; // appends to `s` |
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// |
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// OStringStream is faster to create than std::ostringstream but it's still |
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// relatively slow. Avoid creating multiple streams where a single stream will |
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// do. |
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// |
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// Creates unnecessary instances of OStringStream: slow. |
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// |
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// std::string s; |
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// OStringStream(&s) << 42; |
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// OStringStream(&s) << ' '; |
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// OStringStream(&s) << 3.14; |
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// |
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// Creates a single instance of OStringStream and reuses it: fast. |
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// |
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// std::string s; |
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// OStringStream strm(&s); |
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// strm << 42; |
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// strm << ' '; |
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// strm << 3.14; |
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// |
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// Note: flush() has no effect. No reason to call it. |
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class OStringStream : private std::basic_streambuf<char>, public std::ostream { |
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public: |
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// The argument can be null, in which case you'll need to call str(p) with a |
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// non-null argument before you can write to the stream. |
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// |
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// The destructor of OStringStream doesn't use the std::string. It's OK to destroy |
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// the std::string before the stream. |
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explicit OStringStream(std::string* s) : std::ostream(this), s_(s) {} |
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std::string* str() { return s_; } |
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const std::string* str() const { return s_; } |
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void str(std::string* s) { s_ = s; } |
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private: |
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using Buf = std::basic_streambuf<char>; |
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Buf::int_type overflow(int c = Buf::traits_type::eof()) override { |
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assert(s_); |
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if (!Buf::traits_type::eq_int_type(c, Buf::traits_type::eof())) |
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s_->push_back(static_cast<char>(c)); |
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return 1; |
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} |
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std::streamsize xsputn(const char* s, std::streamsize n) override { |
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assert(s_); |
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s_->append(s, n); |
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return n; |
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} |
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std::string* s_; |
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}; |
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} // namespace strings_internal |
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} // namespace absl |
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#endif // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
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