Question

我对C ++很新，并且使用它创建类，特别是使用模板类。我收到了很多错误消息，我不知道如何修复它们，希望有人能提供帮助，提前谢谢。

班级：

template <class T> class Vector {
    public:
        typedef T* iterator;
        Vector();
        iterator begin();
        iterator end();
        int size();
        iterator insert(iterator position, const T& item);
        void alloc_new();

    private:
        T items;
        int used;      
};

template <class T> Vector::Vector() { 
    items = [1000];
    used = 0;
}

template <class T> iterator Vector::begin() {
   return items; 
}

template <class T> iterator Vector::end(){
    return items + used;
}

template <class T> int Vector::size() {
    return used;
}

template <class T> iterator Vector::insert(iterator position, const T& item){

    if (used+1 > items){
        alloc_new();}  

    items[position] = item;
    used =+ 1;

}

template <class T> void Vector::alloc_new(){
        items = used*2;
        T tmp[] = items;

        for (int i = 0; i < used; i++){
            tmp[i] = items[i];
        } 
        delete items;
        items = tmp;
    }

错误消息：

main.cpp:67: error: `template class Vector' used without template parameters
main.cpp:67: error: ISO C++ forbids declaration of `Vector' with no type
main.cpp:67: error: declaration of template `template int Vector()'
main.cpp:52: error: conflicts with previous declaration `template class Vector'
main.cpp:52: error: previous non-function declaration `template class Vector'
main.cpp:67: error: conflicts with function declaration `template int Vector()'
main.cpp: In function `int Vector()':
main.cpp:68: error: `items' undeclared (first use this function)
main.cpp:68: error: (Each undeclared identifier is reported only once for each function it appears in.)
main.cpp:68: error: expected primary-expression before '[' token
main.cpp:69: error: `used' undeclared (first use this function)
main.cpp: At global scope:
main.cpp:72: error: expected constructor, destructor, or type conversion before "Vector"
main.cpp:72: error: expected `;' before "Vector"
main.cpp:76: error: expected constructor, destructor, or type conversion before "Vector"
main.cpp:76: error: expected `;' before "Vector"
main.cpp:80: error: `template class Vector' used without template parameters
main.cpp: In function `int size()':
main.cpp:81: error: `used' undeclared (first use this function)
main.cpp: At global scope:
main.cpp:84: error: expected constructor, destructor, or type conversion before "Vector"
main.cpp:84: error: expected `;' before "Vector"
main.cpp:94: error: `template class Vector' used without template parameters
main.cpp: In function `void alloc_new()':
main.cpp:95: error: `items' undeclared (first use this function)
main.cpp:95: error: `used' undeclared (first use this function)

Answer 1

您需要指定模板参数。例如：

template <class T> Vector<T>::Vector() { 
    items = [1000];  // note, this is also invalid syntax
    used = 0;
}

Answer 2

Vector::vector()需要更改为Vector<T>::vector()。以下成员函数也是如此。
iterator需要以Vector<T>作为Vector<T>::iterator，因为iterator已在类Vector内声明

Answer 3

因为迭代器是Vector的嵌套类型，所以改变

template <class T> iterator Vector::begin() { return items; }

到

template <typename T> Vector<T>::iterator Vector<T>::begin() { return items; }

也可以使用涉及迭代器的所有其他方法。

创建我自己的矢量类，很多错误

3 个答案: