copy_if的正确实现

// 一个copy_if的正确实现 template<typename InputIterator, typename OutputIterator, typename Predicate> OutputIterator copy_if( InputIterator begin, InputIterator end, OutputIterator destBegin, Predicate p) { while (begin != end) { if (p(*begin)) *destBegin++ = *begin; ++begin; } return destBegin; }