set_new_handler

std::set_new_handler 用於若是 new 失敗就調用此函數;

int * gmem = 0;
void outofmem()
{
    std::cerr << "mem alloc failed" << endl;
    Sleep(500);  //稍微睡一下,否則中止調式按鈕都沒反映啦
}

int main(int argc, char *argv[])
{
    enum { Chunk = 1024 * 1024 * 8 };
    std::set_new_handler(outofmem);
    gmem = new int[100000000000 * Chunk];  //一旦失敗調用outofmem. 不斷的調用


    return 0;
}

只要new 失敗則一直調用此函數 , 直到有足夠的內存爲止, 意圖在讓你去釋放一些內存;

set_new_handler(0); 用來還原

若是有需求通常寫一個父類去實現:

class MemHandler{   //用於還原handler
public:
    MemHandler(std::new_handler handler) :handler(handler){}
    ~MemHandler(){ std::set_new_handler(handler);}
private:
    MemHandler(const MemHandler &) ;
    MemHandler & operator = (const MemHandler &);
    std::new_handler handler;
};

//也能夠把此類寫成 template <typename T>
class NewHandlerBaseClass{
public:
    static std::new_handler setNewHandler(std::new_handler newhandler)    throw()
    {
        std::new_handler old_hanlder = m_handler;
        m_handler = newhandler;
        return old_hanlder;
    }
    
    //重載一個
    static void * operator new (std::size_t size) throw (std::bad_alloc){
            MemHandler memhandler(std::set_new_handler(m_handler));  //設置handler
            return ::operator new(size); //仍是調用原來的new
    }
private:
    static std::new_handler m_handler;
};


//若是上面的類是模版的話 . 每一個類都有一個獨立的static m_handler;
class XClass : public NewHandlerBaseClass<XClass>
{
    ....
};