CODEWITHSUNDEEP
c++structlinked-list
Moj
Moj

Reputation: 6361

iterate through list of linked list

I am kind of new to c++ and got headache with this pointer and stuff!

I need to iterate through list of struct which is linked list, read the data of struct and pop that entry!

this my struct :

struct node {
    map<string,double> candidates;
    double pathCost;
    string source;
    node *next;             // the reference to the next node
};

by reading this post I create my list like :

list<node*> nodeKeeper;

and then initialized the first value:

    node *head;
    head= new node;
    head->pathCost = 0.0;
    head->source="head";
    head->next = NULL;

thin fill the list and struct :

for(unsigned int i = 0; i < sourceSentence.size(); i++){

    node *newNode= new node;             //create a temporary node


    //DO STUFF HERE


    //push currunt node to stack
    nodeKeeper.push_back(newNode);

    head = newNode;

}

now I have list of struct and I want to iterate through it and pop the elements:

for (list<node*>::const_iterator it=nodeKeeper.begin();it!=nodeKeeper.end();it++){

    it->pop_front();

}

which gives me this error:

error: request for member 'pop_front' in '* it.std::_List_const_iterator<_Tp>::operator->()', which is of pointer type 'node* const' (maybe you meant to use '->' ?) make: *** [main3.o] Error 1

It looks like that my iterator points inside the list , not the list itself!

Can you tell me what is wrong here?!

Upvotes: 0

Views: 9178

Answers (2)

David G
David G

Reputation: 96810

If all you need to do is remove the elements, use std::list::clear:

nodeKeeper.clear();

To read the contents of the element, then remove, try this:

for (std::list<node*>::const_iterator it = nodeKeeper.begin(); it != nodeKeeper.end(); ++it) {
    std::cout << (*it)->source;
    // do more reading

    nodeKeeper.pop_front();
}

or with C++11:

for (const auto& a : nodeKeeper) {
    std::cout << a->source;

    nodeKeeper.pop_front();
}

Upvotes: 2

Robert Prior
Robert Prior

Reputation: 508

If your goal is to have a single list of your node struct, there is no need to manage next pointers your self. Inserting would stay the same (minus the head = line)

To pop all element of the list you would do something like 

int sizeOfList = nodeKeeper.size();
for( int i =0; i < sizeOfList; i++) {
    //if you want to do something with the last element
    node * temp = nodeKeeper.back();
    //do stuff with that node

    //done with the node free the memory
    delete temp;
    nodeKeeper.pop_back();
}

Compiling/running example here: http://ideone.com/p6UlyN

Upvotes: 2

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