3

你能解释一下下面代码的输出吗？我需要做什么才能调用正确的基类构造函数？

谢谢。

#include <vector>
#include <iostream>

template <class CONTAINER> class SequenceComposite {
protected:
    CONTAINER m_data;
public:
    typedef typename CONTAINER::value_type value_type;
    typedef typename CONTAINER::allocator_type allocator_type;
    typedef typename CONTAINER::size_type size_type;
    explicit SequenceComposite(const allocator_type& alloc = allocator_type()) : m_data(alloc) {
        std::cout << std::endl << "SequenceComposite(alloc)" << std::endl;
    }
    explicit SequenceComposite(size_type n, const value_type& val = value_type(),
        const allocator_type& alloc = allocator_type()) : m_data(n, val, alloc) {
        std::cout << std::endl << "SequenceComposite(n, val, alloc)" << std::endl;
    }
    SequenceComposite(const SequenceComposite& x) : m_data(x.m_data) {
        std::cout << std::endl << "SequenceComposite(x)" << std::endl;
    }

};

template <class DTYPE>
class VectorComposite : public virtual SequenceComposite< std::vector<DTYPE> > {
public:
    typedef typename VectorComposite::value_type value_type;
    typedef typename VectorComposite::allocator_type allocator_type;
    typedef typename VectorComposite::size_type size_type;
    explicit VectorComposite(const allocator_type& alloc = allocator_type()) : SequenceComposite< std::vector<DTYPE> >(alloc) {
        std::cout << "VectorComposite(alloc)" << std::endl;
    }
    explicit VectorComposite(size_type n, const value_type& val = value_type(),
        const allocator_type& alloc = allocator_type()) : SequenceComposite< std::vector<DTYPE> >(n, val, alloc) {
        std::cout << "VectorComposite(n, val, alloc)" << std::endl;
    }
    VectorComposite(const VectorComposite& x) : SequenceComposite< std::vector<DTYPE> >(x) {
        std::cout << "VectorComposite(x)" << std::endl;
    }

};

template<typename T> class MyModel : public virtual VectorComposite<T> {
    public:
        MyModel() {
            std::cout << "MyModel()" << std::endl;
        };
        MyModel(const MyModel<T> &vec) : VectorComposite<T>(vec) {
            std::cout << "MyModel(x)" << std::endl;
        }
        MyModel( size_t n, const T& value= 0) : VectorComposite<T>(n, value) {
            std::cout << "MyModel(n, val)" << std::endl;
        }
};

int main() {
    MyModel<float> c(4, 2.0);
    MyModel<float> e(c);

    VectorComposite<float> a(3, 2.0);
    VectorComposite<float> b(c);

    return 0;
}

输出：

SequenceComposite(alloc)
VectorComposite(n, val, alloc)
MyModel(n, val)

SequenceComposite(alloc)
VectorComposite(x)
MyModel(x)

SequenceComposite(n, val, alloc)
VectorComposite(n, val, alloc)

SequenceComposite(x)
VectorComposite(x)

我期望

SequenceComposite(n, val, alloc)
VectorComposite(n, val, alloc)
MyModel(n, val)

SequenceComposite(x)
VectorComposite(x)
MyModel(x)
...
4

1 回答 1

2

虚拟基类从最派生类型的构造函数初始化。所以在前两个示例中，SequenceComposite调用了默认构造函数。那就是allocator_type带有默认参数的那个。要使用不同的构造函数，请从最派生类型的初始值设定项列表中调用它。

于 2013-03-14T14:45:48.267 回答