Uncertainties about OOP and the struct Keyword-CodePudding

class NodeType { 
 public: 
    int info; 
    NodeType* link; 
};

I came across this when learning about linked list, and as a beginner, at line 4, pointer link is an object of class NodeType, this interpretation is definitely wrong, so can somebody please explain what does this line mean? I don't recall learning this when I am interacting with the concept of OOP.

struct NodeType 
{ 
    int info; 
    struct NodeType* link; 
};

I take that this structure declaration here is of the same as the class declared above, so my second question is, why is there a second struct keyword at line 4? Can the keyword be removed? Is this the phenomenon called nested struct?

CodePudding user response：

Yes, the two snippets are the same.

why is there a second struct keyword at line 4?

It's called an elaborated type specifier (a type with struct prepended to it, or class/union/enum; the definition class NodeType {} doesn't count as one).

It's useless here and can be removed. It's only useful when a struct is mentioned for the first time, so the compiler doesn't know it's a struct yet.

In this regard C is different from C, where you must prepend struct every time to refer to a struct.

[is] pointer link is an object of class NodeType?

No, an object of class NodeType would be NodeType link;, but then it wouldn't be a pointer.

You could say that link is an object of type NodeType * (a pointer to NodeType).