小编hon*_*iao的帖子

class A
{
public:
    A(){}
    virtual void func();
};
class B:public A
{
    void func(){}
}

如果func未实现,则在定义一个对象时会出现链接错误A.所以为什么？我没打电话func.

template<class _Diff,
        class _Urng>
        class _Rng_from_urng
    {   // wrap a URNG as an RNG
    public:
        explicit _Rng_from_urng(_Urng& _Func)
            : _Ref(_Func), _Bits(CHAR_BIT * sizeof(_Udiff)), _Bmask(_Udiff(-1))
        {   // construct from URNG
            for (; (_Urng::max)() - (_Urng::min)() < _Bmask; _Bmask >>= 1)
                --_Bits;
        }

        _Diff operator()(_Diff _Index)
        {   // adapt _Urng closed range to [0, _Index)
            for (;;)
            {   // try a sample random value
                _Udiff _Ret = 0;    // random bits
                _Udiff _Mask = 0;   // 2^N - 1, _Ret is within …