Define a struct inside a class in C++

Question

Can someone give me an example about how to define a new type of struct in a class in C++.

Thanks.

Answer 1

Yes you can. In c++, class and struct are kind of similar. We can define not only structure inside a class, but also a class inside one. It is called inner class.

As an example I am adding a simple Trie class.

class Trie {
private:
    struct node{
        node* alp[26];
        bool isend;
    };
    node* root;
    node* createNode(){
        node* newnode=new node();
        for(int i=0; i<26; i++){
            newnode->alp[i]=nullptr;
        }
        newnode->isend=false;
        return newnode;
    }
public:
    /** Initialize your data structure here. */
    Trie() {
        root=createNode();
    }

    /** Inserts a word into the trie. */
    void insert(string word) {
        node* head=root;
        for(int i=0; ialp[int(word[i]-'a')]==nullptr){
                node* newnode=createNode();
                head->alp[int(word[i]-'a')]=newnode;
            }
            head=head->alp[int(word[i]-'a')];
        }
        head->isend=true;
    }

    /** Returns if the word is in the trie. */
    bool search(string word) {
        node* head=root;
        for(int i=0; ialp[int(word[i]-'a')]==nullptr){
                return false;
            }
            head=head->alp[int(word[i]-'a')];
        }
        if(head->isend){return true;}
        return false;
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    bool startsWith(string prefix) {
        node* head=root;
        for(int i=0; ialp[int(prefix[i]-'a')]==nullptr){
                return false;
            }
            head=head->alp[int(prefix[i]-'a')];
        }
        return true;
    }
};

/**
 * Your Trie object will be instantiated and called as such:
 * Trie* obj = new Trie();
 * obj->insert(word);
 * bool param_2 = obj->search(word);
 * bool param_3 = obj->startsWith(prefix);
 */