c++ - struct _stack* 和 Digit::struct_stack* 中的一些问题

Question

void Digit::push(int value){

    struct _stack *next_field = new struct _stack;
    if (end == nullptr && start == nullptr){
        next_field->_next_ptr = nullptr; //in codebloks project. next_ptr = himself
        start = next_field;
    }
    else
        next_field->_next_ptr = end;
    next_field->_data = value;
    end = next_field;
}

出现的错误是:

assigning to 'struct _stack *' (aka '_stack *') from incompatible type 'struct _stack *' (aka 'Digit::_stack *')

我该如何解决？

这是 Header Digit 类:

class Digit
{
    struct _stack *start = nullptr;
    struct _stack *end = nullptr;
    struct _stack *ptr_element = nullptr;

    struct _stack {
        _stack* _next_ptr = nullptr;
        int _data = 0;
    }_element;

public:
    Digit();
    void push(int);
    void pop();
};

Answer 1

编译器将 class Digit 中的 struct _stack 和 struct _stack 视为两个不同的实体。

要解决此问题，请在指针声明之前移动 class Digit 中的 struct _stack 定义。该类应如下所示:

class Digit
{
    struct _stack {
        _stack* _next_ptr = nullptr;
        int _data = 0;
    }_element;

    struct _stack *start = nullptr;
    struct _stack *end = nullptr;
    struct _stack *ptr_element = nullptr;   

public:
    Digit();
    void push(int);
    void pop();
};

See Demo