我希望做的是创造一种“管道”（如进程之间的管道），但在同一程序中℃之间++ iostreams的。 我有一个需要输入流作为自变量的函数，但我的数据是从输出流的到来。 那么，有没有管道标准的方式输出std::ostream成输入std::istream ？
Answer 1:
您可以创建一个std::streambuf ，其中输出均进入一个缓冲和std::overflow()时缓冲区已满块。 在另一端，你不得不对其中的块输入缓冲区underflow()当缓冲区变空。 显然，阅读和写作将是两个不同的线程。
最棘手的业务是如何将两个缓冲区同步：在访问缓存的流不使用任何同步操作。 任何的虚函数被调用时，才可以拦截操作和处理的同步。 在另一方面，不使用缓冲区是相当低效的。 我将解决这个问题的方法是通过使用相对小的输出缓冲器（例如256个char或多个），并且还覆盖sync()来使用此功能的字符传送到输入缓冲器。 所述streambuf将使用一个互斥用于同步和条件变量到框上输出一个完整的输入缓冲器和输入一个空的输入缓冲器。 为了支持正常关机也应该有一个功能设置，没有更多的输入快到了，所有进一步的输出操作应该失败的标志。
创建实际的实施表明，两个缓冲器是不够的：访问输入和输出缓冲器的螺纹可以是活动的时相应的其他缓存块。 因此，需要三分之一，中间缓冲器。 有了这个小改动上述计划，下面是一些代码（它使用微小的缓冲区，以确保有实际的溢出和下溢;对于实际使用至少输入缓冲区可能应该更大）。
// threadbuf.cpp -*-C++-*-
// ----------------------------------------------------------------------------
// Copyright (C) 2013 Dietmar Kuehl http://www.dietmar-kuehl.de
//
// Permission is hereby granted, free of charge, to any person
// obtaining a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without restriction,
// including without limitation the rights to use, copy, modify,
// merge, publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
// ----------------------------------------------------------------------------
#include <algorithm>
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <thread>
// ----------------------------------------------------------------------------
class threadbuf
: public std::streambuf
{
private:
typedef std::streambuf::traits_type traits_type;
typedef std::string::size_type string_size_t;
std::mutex d_mutex;
std::condition_variable d_condition;
std::string d_out;
std::string d_in;
std::string d_tmp;
char* d_current;
bool d_closed;
public:
threadbuf(string_size_t out_size = 16, string_size_t in_size = 64)
: d_out(std::max(string_size_t(1), out_size), ' ')
, d_in(std::max(string_size_t(1), in_size), ' ')
, d_tmp(std::max(string_size_t(1), in_size), ' ')
, d_current(&this->d_tmp[0])
, d_closed(false)
{
this->setp(&this->d_out[0], &this->d_out[0] + this->d_out.size() - 1);
this->setg(&this->d_in[0], &this->d_in[0], &this->d_in[0]);
}
void close()
{
{
std::unique_lock<std::mutex> lock(this->d_mutex);
this->d_closed = true;
while (this->pbase() != this->pptr()) {
this->internal_sync(lock);
}
}
this->d_condition.notify_all();
}
private:
int_type underflow()
{
if (this->gptr() == this->egptr())
{
std::unique_lock<std::mutex> lock(this->d_mutex);
while (&this->d_tmp[0] == this->d_current && !this->d_closed) {
this->d_condition.wait(lock);
}
if (&this->d_tmp[0] != this->d_current) {
std::streamsize size(this->d_current - &this->d_tmp[0]);
traits_type::copy(this->eback(), &this->d_tmp[0],
this->d_current - &this->d_tmp[0]);
this->setg(this->eback(), this->eback(), this->eback() + size);
this->d_current = &this->d_tmp[0];
this->d_condition.notify_one();
}
}
return this->gptr() == this->egptr()
? traits_type::eof()
: traits_type::to_int_type(*this->gptr());
}
int_type overflow(int_type c)
{
std::unique_lock<std::mutex> lock(this->d_mutex);
if (!traits_type::eq_int_type(c, traits_type::eof())) {
*this->pptr() = traits_type::to_char_type(c);
this->pbump(1);
}
return this->internal_sync(lock)
? traits_type::eof()
: traits_type::not_eof(c);
}
int sync()
{
std::unique_lock<std::mutex> lock(this->d_mutex);
return this->internal_sync(lock);
}
int internal_sync(std::unique_lock<std::mutex>& lock)
{
char* end(&this->d_tmp[0] + this->d_tmp.size());
while (this->d_current == end && !this->d_closed) {
this->d_condition.wait(lock);
}
if (this->d_current != end)
{
std::streamsize size(std::min(end - d_current,
this->pptr() - this->pbase()));
traits_type::copy(d_current, this->pbase(), size);
this->d_current += size;
std::streamsize remain((this->pptr() - this->pbase()) - size);
traits_type::move(this->pbase(), this->pptr(), remain);
this->setp(this->pbase(), this->epptr());
this->pbump(remain);
this->d_condition.notify_one();
return 0;
}
return traits_type::eof();
}
};
// ----------------------------------------------------------------------------
static void writer(std::ostream& out)
{
for (std::string line; std::getline(std::cin, line); )
{
out << "writer: '" << line << "'\n";
}
}
// ----------------------------------------------------------------------------
static void reader(std::istream& in)
{
for (std::string line; std::getline(in, line); )
{
std::cout << "reader: '" << line << "'\n";
}
}
// ----------------------------------------------------------------------------
int main()
{
try
{
threadbuf sbuf;
std::ostream out(&sbuf);
std::istream in(&sbuf);
std::thread write(&::writer, std::ref(out));
std::thread read(&::reader, std::ref(in));
write.join();
sbuf.close();
read.join();
}
catch (std::exception const& ex)
{
std::cerr << "ERROR: " << ex.what() << "\n";
}
}
文章来源: c++ connect output stream to input stream
