模板初始化：

Question

我想从 Matrix 类创建行向量和列向量别名。我该怎么做？

template<class T, unsigned int m, unsigned int n>
class Matrix {
public:
    Matrix();

    .
    .
    .

private:
    unsigned int rows;
    unsigned int cols;
    .
};

我在这里得到错误。我看到模板的类型别名无法完成。有什么办法可以处理吗？对于下面我得到错误为“别名模板的部分专业化”。

template<class T, unsigned int m, unsigned int n>
using rowVector<T,n> = Matrix<T,1,n>;

template<class T, unsigned int m, unsigned int n>
using colVector<T,m> = Matrix<T,m,1>;

任何指针我该如何做到这一点？

Answer 1

这是正确的语法：

template <class T, unsigned int n>
using rowVector = Matrix<T, 1, n>;

template <class T, unsigned int m>
using colVector = Matrix<T, m, 1>;

Answer 2

我相信你的代码肯定比你发布的要多，因为这个

template<class T, unsigned int m, unsigned int n>
class Matrix {};

template<class T, unsigned int m, unsigned int n>
using rowVector<T,n> = Matrix<T,1,n>;

template<class T, unsigned int m, unsigned int n>
using colVector<T,m> = Matrix<T,m,1>;

导致以下错误

prog.cc:5:16: error: expected '=' before '<' token
 using rowVector<T,n> = Matrix<T,1,n>;
                ^
prog.cc:5:16: error: expected type-specifier before '<' token
prog.cc:8:16: error: expected '=' before '<' token
 using colVector<T,m> = Matrix<T,m,1>;
                ^
prog.cc:8:16: error: expected type-specifier before '<' token

alias template 的正确语法是：

template < template-parameter-list >
using identifier attr(optional) = type-id ;

所以解决方法是

template<class T, unsigned int m, unsigned int n>
using rowVector = Matrix<T,1,n>;

template<class T, unsigned int m, unsigned int n>
using colVector = Matrix<T,m,1>;

我想你想删除 m 作为 rowVector 的参数和 n 作为 colVector 的参数：

template<class T, unsigned int n>
using rowVector = Matrix<T,1,n>;

template<class T, unsigned int m>
using colVector = Matrix<T,m,1>;