问性病的过载处理：：endl？

EN

1. This calls the virtual method `sync()`
2. Override this virtual method to do the work you want.

#include <iostream>
#include <sstream>

class MyStream: public std::ostream
{
    // Write a stream buffer that prefixes each line with Plop
    class MyStreamBuf: public std::stringbuf
    {
        std::ostream&   output;
        public:
            MyStreamBuf(std::ostream& str)
                :output(str)
            {}
            ~MyStreamBuf() {
                if (pbase() != pptr()) {
                    putOutput();
                }
            }
   
        // When we sync the stream with the output. 
        // 1) Output Plop then the buffer
        // 2) Reset the buffer
        // 3) flush the actual output stream we are using.
        virtual int sync() {
            putOutput();
            return 0;
        }
        void putOutput() {
            // Called by destructor.
            // destructor can not call virtual methods.
            output << "[blah]" << str();
            str("");
            output.flush();
        }
    };

    // My Stream just uses a version of my special buffer
    MyStreamBuf buffer;
    public:
        MyStream(std::ostream& str)
            :std::ostream(&buffer)
            ,buffer(str)
        {
        }
};


int main()
{
    MyStream myStream(std::cout);
    myStream << 1 << 2 << 3 << std::endl << 5 << 6 << std::endl << 7 << 8 << std::endl;
}

> ./a.out
[blah]123 
[blah]56 
[blah]78
>

MyStream& operator<<( std::ostream&(*f)(std::ostream&) )
{
    std::cout << f;

    if( f == std::endl )
    {
        _lastTokenWasEndl = true;
    }

    return *this;
}

flush(__os.put(__os.widen('\n')));