使用boost :: iostreams :: tee_device？ [英] Using boost::iostreams::tee_device?

问题描述

有人可以帮我吗？

我想尝试做以下事情：

#include <boost/iostreams/tee.hpp>
#include <boost/iostreams/stream.hpp>
#include <sstream>  
#include <cassert>  

namespace io = boost::iostreams;
typedef io::stream<io::tee_device<std::stringstream, std::stringstream> > Tee;
std::stringstream ss1, ss2;
Tee my_split(ss1, ss2); // redirects to both streams
my_split << "Testing";
assert(ss1.str() == "Testing" && ss1.str() == ss2.str());

但它不会在VC9中编译：

But it won't compile in VC9:

c:\lib\boost_current_version\boost\iostreams\stream.hpp(131) : error C2665: 'boost::iostreams::tee_device<Sink1,Sink2>::tee_device' : none of the 2 overloads could convert all the argument types

上班？我知道我可以让自己的类来做，但我想知道我做错了什么。

Has anyone gotten this to work? I know I could make my own class to do it, but I want to know what I am doing wrong.

感谢

推荐答案

您可以使用 io :: stream 的通用％5Fstreams.html＃stream％5Fforwarding％5Fconstructors> constructor-forwarding版本论据。 C ++ 03只有有限的功能，当涉及到转发函数的参数（需要的重载量需要容易地成指数增长）。它（ io :: stream ）有以下限制：

You use the constructor-forwarding version of io::stream, which construct a tee-stream itself and forward all arguments to that. C++03 has only limited capabilities when it comes to forwarding arguments to functions (amount of overloads needed easily grow exponentially). It (io::stream) makes the following restrictions:

成员构造流的实例，并将其与从给定的参数列表构建的Device T的实例相关联。

好吧，但是<$> c $ c> tee_device 构造函数

根据给定的Sink对构造tee_device的实例。如果相应的模板参数是流或流缓冲区类型，则每个函数参数是非常量引用，否则为const引用。

Constructs an instance of tee_device based on the given pair of Sinks. Each function parameter is a non-const reference if the corresponding template argument is a stream or stream buffer type, and a const reference otherwise.

当然不会工作。 io :: stream 提供另一个构造函数，它使用 T 作为第一个参数。这个工作在这里（至少编译，断言，虽然，我没有使用 boost :: iostreams ，所以我不能帮助）

That won't work, of course. io::stream provides another constructor that takes a T as first argument. This works here (Compiles, at least. The assertion fails, though. I've not worked with boost::iostreams so i can't help with that)

namespace io = boost::iostreams;
typedef io::tee_device<std::stringstream, std::stringstream> TeeDevice;
typedef io::stream< TeeDevice > TeeStream;
std::stringstream ss1, ss2;
TeeDevice my_tee(ss1, ss2); 
TeeStream my_split(my_tee);
my_split << "Testing";
assert(ss1.str() == "Testing" && ss1.str() == ss2.str());

编辑：调用 flush（）流<< std :: flush ，断言通过。

After calling flush() or streaming << std::flush, the assertion passes.

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