Abseil Common Libraries (C++) (grcp 依赖)
https://abseil.io/
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
98 lines
2.9 KiB
98 lines
2.9 KiB
7 years ago
|
// 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 {
|
||
|
|
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 = Buf::traits_type::eof()) override {
|
||
|
|
assert(s_);
|
||
|
|
if (!Buf::traits_type::eq_int_type(c, Buf::traits_type::eof()))
|
||
|
|
s_->push_back(static_cast<char>(c));
|
||
|
|
return 1;
|
||
|
|
}
|
||
|
|
|
||
|
|
std::streamsize xsputn(const char* s, std::streamsize n) override {
|
||
|
|
assert(s_);
|
||
|
|
s_->append(s, n);
|
||
|
|
return n;
|
||
|
|
}
|
||
|
|
|
||
|
|
std::string* s_;
|
||
|
|
};
|
||
|
|
|
||
|
|
} // namespace strings_internal
|
||
|
|
} // namespace absl
|
||
|
|
|
||
|
|
#endif // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
|