如何从C ++ std :: basic_ostream派生并使<<操作员虚拟的? [英] How to derive from C++ std::basic_ostream and make the << operator virtual?

问题描述

我正在编写一个具有各种消息输出的类.我想使此类与通用类和平台无关，因此我想对它传递 basic_ostream 引用，它可以将所有消息转储到流中.这样，如果在控制台程序中使用了该类，则可以将 std :: cout 传递给它并显示在控制台窗口中.

I am writing a class that has various messages output. I want to make this class general and platform independent, so I am thinking of passing a basic_ostream reference to it and it can dump all the messages into the stream. By doing this, if the class is used in a console program, I can pass std::cout to it and display in console window.

或者我可以将派生的ostream传递给它，然后将消息重定向到某些UI组件，例如列表框?唯一的问题是数据插入器operator <<不是虚函数.如果我将派生类引用传递给它，则只有 basic_ostream <<运算符将被调用.

Or I could pass a derived ostream to it and redirect the message to some UI components, e.g. ListBox? The only problem is the data inserter operator << is not a virtual function. If I pass the derived class reference to it, only the basic_ostream << operator will be called.

有什么解决方法吗?

推荐答案

张楠自己的答案，最初是作为问题的一部分发布的:

跟进:好的，这是实现所需功能的派生std :: streambuf:

Follow up: OK, here is the derived std::streambuf that implements required functionality:

class listboxstreambuf : public std::streambuf { 
public:
    explicit listboxstreambuf(CHScrollListBox &box, std::size_t buff_sz = 256) :
            Scrollbox_(box), buffer_(buff_sz+1) {
        char *base = &buffer_.front();
        //set putbase pointer and endput pointer
        setp(base, base + buff_sz); 
    }

protected:
    bool Output2ListBox() {
        std::ptrdiff_t n = pptr() - pbase();
        std::string temp;
        temp.assign(pbase(), n);
        pbump(-n);
        int i = Scrollbox_.AddString(temp.c_str());
        Scrollbox_.SetTopIndex(i);
        return true;
    }

private:
    int sync() {
        return Output2ListBox()? 0:-1;
    }

    //copying not allowed.
    listboxstreambuf(const listboxstreambuf &);
    listboxstreambuf &operator=(const listboxstreambuf &);

    CHScrollListBox &Scrollbox_;
    std::vector<char> buffer_;
};

要使用此类，只需创建一个std :: ostream并使用此缓冲区初始化

To use this class just create a std::ostream and initialize with this buffer

std::ostream os(new listboxstreambuf(some_list_box_object));

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