Repo created

TMessagesProj/jni/voip/webrtc/absl/strings/internal/ostringstream.h

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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
+//
+//      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 {
+ 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* str)
+      : std::ostream(&buf_), buf_(str) {}
+  OStringStream(OStringStream&& that)
+      : std::ostream(std::move(static_cast<std::ostream&>(that))),
+        buf_(that.buf_) {
+    rdbuf(&buf_);
+  }
+  OStringStream& operator=(OStringStream&& that) {
+    std::ostream::operator=(std::move(static_cast<std::ostream&>(that)));
+    buf_ = that.buf_;
+    rdbuf(&buf_);
+    return *this;
+  }
+
+  std::string* str() { return buf_.str(); }
+  const std::string* str() const { return buf_.str(); }
+  void str(std::string* str) { buf_.str(str); }
+
+ private:
+  class Streambuf final : public std::streambuf {
+   public:
+    explicit Streambuf(std::string* str) : str_(str) {}
+    Streambuf(const Streambuf&) = default;
+    Streambuf& operator=(const Streambuf&) = default;
+
+    std::string* str() { return str_; }
+    const std::string* str() const { return str_; }
+    void str(std::string* str) { str_ = str; }
+
+   protected:
+    int_type overflow(int c) override;
+    std::streamsize xsputn(const char* s, std::streamsize n) override;
+
+   private:
+    std::string* str_;
+  } buf_;
+};
+
+}  // namespace strings_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_