CODEWITHSUNDEEP
qtc++11iterator
Jack
Jack

Reputation: 16724

'begin' was not declared in this scope

I have a class like that (I leave only the relevant part):

    template<class T>
    class MyList
    {
    public:
    // ....

    typename QList<T*>::iterator begin()
    {
        return list.begin();
    }

    typename QList<T*>::iterator end()
    {
        return list.end();
    }

    typename QList<T*>::iterator skip(int n)
        {
            auto ite = list.begin();

            while(n --> 0)
                ++ite;

            return ite;
        }

       QList<T*> list;
    };

when I went to use the class:

MyList<Foo*> foo;
for(Foo* f : foo.skip(1)) {

I get this error:

'begin' was not declared in this scope

I remove skip() call, the loop works fine... I don't understand why. Why that and how do I fix this?

Upvotes: 2

Views: 3676

Answers (1)

Dimitrios Bouzas
Dimitrios Bouzas

Reputation: 42939

This is just how range-based for loops work in C++. In particular, when in a range expression the participant is a class type, in your case MyList, for the expression to be legitimate the class type must have defined members begin and end.

Member function MyList::skip returns an iterator to a QList<T*>. This iterator class doesn't define any begin and end members and the compiler renders this type (i.e., the iterator) not a legitimate participant for a range-based for loop expression while the class type MyList that has defined members begin and end renders legitimate.

More info on how a range-for loop works you can find here.

Upvotes: 4

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