将流加倍

Question

我使用cerr流作为我的错误输出，但我也想将这个错误输出保存在内存中的字符串流中。

我想把这件事变成：

stringstream errorString;
cerr << " Something went wrong ";
errorString << " Something went wrong ";

转到

myErr << " Something went wrong ";

其中myErr是一个类的实例，它将其存储在字符串流中，并输出到cerr。

谢谢你的帮助。

Answer 1

您可以像这样创建myErr类的类型：

class stream_fork
{
    std::ostream& _a;
    std::ostream& _b;

public:
    stream_fork( std::ostream& a, std::ostream& b)
        :   _a( a ),
            _b( b )
    {
    }

    template<typename T>
    stream_fork& operator<<( const T& obj )
    {
        _a << obj;
        _b << obj;
        return *this;
    }

    // This lets std::endl work, too!
    stream_fork& operator<<( std::ostream& manip_func( std::ostream& ) )
    {
        _a << manip_func;
        _b << manip_func;
        return *this;
    }
};

用法：

stream_fork myErr( std::cerr, errorString );
myErr << "Error Message" << std::endl;

Answer 2

您可以使用Boost.IOStreams。

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

namespace io = boost::iostreams;

int main() {
    std::stringstream ss;
    io::tee_device<decltype(ss), decltype(std::cerr)> sink(ss, std::cerr);
    io::stream<decltype(sink)> stream(sink);
    stream << "foo" << std::endl;
    std::cout << ss.str().length() << std::endl;
    return 0;
}

Answer 3

覆盖MyErr类中的operator<<

MyErr& operator<< ( MyErr& myErr, std::string message)
{
    cerr << message;
    errorString << message; //Where errorString is a member of the MyErr class

    return myErr;
}

然后，您想要记录错误的位置：

int main()
{
    MyErr myErr;
    myErr << " Something went wrong. ";

    return 0;
}

您可能想让MyErr成为一个单独的类，这样所有写入errorString的东西都可以放在一个地方。