c++ - &token 之前预期的构造函数、析构函数或类型转换

Question

我的项目中出现神秘错误:

expected constructor, destructor, or type conversion

它不允许我使用重载的 operator<< .在我将我的类(class)( myVector )变成 template 之前，这以前是有效的

//MyVector class
//An implementation of a vector of integers.
template <class T>
class MyVector{
public:
    //Purpose: Initialize an object of type MyVector
    //Parameters: none.
    //Returns: nothing.
    MyVector();

    //------------------------------------------------
    //Purpose: Initialize an object of type MyVector
    //Parameters: an integer.
    //Returns: nothing.
    //------------------------------------------------
    MyVector(int);

    //Purpose: Destroys objects of type MyVector
    //Parameters: none.
    //Returns: nothing
    //------------------------------------------------
    ~MyVector();

    //Purpose: Returns the current size of the MyVector.
    //Parameters: none.
    //Returns: the size.
    int size() const;

    //------------------------------------------------
    //Purpose: Returns the capacity of the MyVector.
    //Parameters: none.
    //Returns: int.
    int capacity() const;

    //------------------------------------------------
    //Purpose: Removes the entries of MyVector.
    //Parameters: none.
    //Returns: nothing.
    void clear();

    //------------------------------------------------
    //Purpose: Appends a given integer to the vector.
    //Parameters: an integer.
    //Returns: nothing.
    void push_back(T);

    //------------------------------------------------
    //Purpose: Shows what's at a given position.
    //Parameters: an integer index.
    //Returns: an integer.
    T at(int) const;

    MyVector(const MyVector& b);
    const MyVector& operator=(const MyVector&);

    //------------------------------------------------

private:
    int _size;
    int _capacity;
    int* head;

    //Purpose: Increases the capacity of a MyVector when it's 
    // capacity is equal to it's size. Called by push_back(int)
    //Parameters/Returns: nothing.
    void increase();

    //Purpose: Copies the given vector reference. 
    //Param: MyVector reference.
    //Returns: nothing.
    void copy(const MyVector&);

    //Purpose: Frees MyVector up for an assignment.
    void free();
};

template <class T>
ostream& operator<<(ostream&, const MyVector<T>);
//This line is giving me the error.

#endif

我在一个单独的文件中有运算符(operator)的代码:

template <class T>
ostream& operator<<(ostream& os, const MyVector<T> V){
    int N = V.size();
    os << endl;
    for(int i = 0; i<N; i++){
        os << V.at(i)<<endl;
    }
    return os;
}

我看过其他问题，但似乎没有一个与我的匹配。帮助将不胜感激。谢谢!

Answer 1

您可能需要符合条件 ostream与 std作为:

std::ostream& operator<<(std::ostream&, const MyVector<T>);

而且几乎可以肯定，您应该通过 const 引用而不是 const 值来传递 vector 。