Strange behaviour of typedef in struct

Question

I was making a program of singly linked list in C++ so use of struct inside the class. I know that typedef is used with struct, so that afterwards the declaration does not require use of struct keyword. But when I don't use typedef the code is successfully compiled even without using the struct keyword in future declarations, but when I use typedef it does not compile. Here is the code:

#include <iostream>
using namespace std;

struct node{        
    int data;
    node* next;
}*head; 

class single_list{
    public:
        struct node* create_node(int);
        void insert_begin();
        void insert_pos();
        void insert_last();
        void delete_pos();
        void sort();
        void display();
};

int main()
{
    int choice,nodes,element,position,i;
    single_list sl;
    node* head = NULL;
    while(1)
    {
        cout<<endl<<"List of operations"<<endl;
        cout<<"1: Insert node at the beginning"<<endl;
        cout<<"2: Insert node at a specific position"<<endl;
        cout<<"3: Insert node at the last"<<endl;
        cout<<"4: Delete a node at specific position"<<endl;
        cout<<"5: Sorting the linked list"<<endl;
        cout<<"6: Display the linked list"<<endl;
        cout<<"Enter your choice"<<endl;
        cin>>choice;

        switch(choice)
        {
            case 1:
                cout<<"Inserting node at the beninning"<<endl;
                sl.insert_begin();
                cout<<endl;
                break;

            case 2:
                cout<<"Inserting node at a specific position"<<endl;
                sl.insert_pos();
                cout<<endl;
                break;

            case 3:
                cout<<"Inserting node at the last place"<<endl;
                sl.insert_last();
                cout<<endl;
                break;

            case 4:
                cout<<"Deleting node at specific position"<<endl;
                sl.delete_pos();
                cout<<endl;
                break;

            case 5:
                cout<<"Sorting the linked list"<<endl;
                sl.sort();
                cout<<endl;
                break;

            case 6:
                cout<<"Displaying the linked list"<<endl;
                sl.display();
                cout<<endl;
                break;

            default:
                cout<<"Wrong Choice"<<endl;                     
        }
    }
}

node *single_list::create_node(int data)
{
    node* temp;
    temp = new node;
    temp->data = data;
    temp->next = NULL;
    return temp;
}

void single_list::insert_begin()
{
    cout<<"Enter value to be inserted"<<endl;
    int data;
    cin>>data;
    node* temp;
    node* p;
    temp = create_node(data);

    if (head == NULL)
    {
        head = temp;
        head->next = NULL;
    }
    else
    {
        p = head;
        head = temp;
        head->next = p;
    }
}

void single_list::insert_pos()
{
    cout<<"Enter the position at which you want to enter the number"<<endl;
    int pos;
    cin>>pos;
    cout<<"Enter the data of the node"<<endl;
    int data;
    node* t;
    t = head;
    node* temp1;
    temp1->data = data;
    for(int i=1;i<pos;i++)
    {
        t = t->next;
    }
    if(pos == 1)
    {
        if(head == NULL)
        {
            head = temp1;
            head->next = NULL;
        }
        else
        {
            temp1->next = t->next;
            t->next = temp1;    
        }
    }
    else
    {
        cout<<"Position out of range"<<endl;
    }

}

void single_list::insert_last()
{
    cout<<"Enter the data of the number"<<endl;
    int data;
    cin>>data;
    node* temp1;
    temp1->data = data;
    temp1->next = NULL;
    node* t;
    t = head;
    while(t != NULL)
   {
        t = t->next;
   }
    t->next = temp1;
}

score 1 · Accepted Answer · answered Mar 22 '16 at 05:28

After you define a struct

struct node{        
    int data;
    node* next;
}*head;

The name node can be used without a typedef in C++. You must be thinking of C, which requires a typedef.

In C++, it is OK to use:

struct node{        
    int data;
    node* next;
};

node* head;

In C, you'll need to use:

struct node{        
    int data;
    struct node* next;
};

struct node* head;

or

// Define the struct and a typedef in one statement.
typedef struct node{        
    int data;
    struct node* next;
} node;

node* head;

Thanks. ya bit confused with C and C++ because my style of writing code in C++ is C with classes — ashish, Mar 22 '16 at 05:33

score 0 · Answer 2 · answered Mar 22 '16 at 05:26

0

You don't need to use struct keyword when defining/declaring an object in C++. It's that way in C not in C++.

answered Mar 22 '16 at 05:26

ixSci

13,100
5
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for defining a new node should we not use **struct node* n** when not defining typedef – ashish Mar 22 '16 at 05:30
@ashish, you can use it but you as well may omit it. It is not required in C++ – ixSci Mar 22 '16 at 05:30

score 0 · Answer 3 · answered Mar 22 '16 at 05:27

The following code declares head to be a pointer to node variable.

struct node{        
    int data;
    node* next;
}*head;

However, the following will define head to be an alias for the type pointer to node.

typedef struct node{        
    int data;
    node* next;
}*head;

Strange behaviour of typedef in struct

3 Answers3