C++ iterator for map derived class

Question

I have a class that internally has an instance of map:

template<typename K, typename V>
class my_map {
    private:
        std::map<K, V> mmap;

Internally to the class I need to create an iterator for templated types, how can I do this?

You want an internal variable that is an iterator to the contained map? — Adrian Mole, Jul 15 '22 at 11:24
Yes, in my internal methods I want to create an interator to the map using the types K,V ? — SPlatten, Jul 15 '22 at 11:25
the question is unclear. whats the problem? `mmap.begin()` is an iterator, `mmap.end()` another one — 463035818_is_not_an_ai, Jul 15 '22 at 11:26
Declare a member variable like this: `decltype(mmap.begin()) myIterator;` ?? — Adrian Mole, Jul 15 '22 at 11:27
@463035818_is_not_a_number, what's unclear, the class can be declared with any types for K or V and internally I want to create iterators using those. — SPlatten, Jul 15 '22 at 11:28
its not clear what problem you encountered. As I wrote, `mmap.begin()` is an iterator, there you go... — 463035818_is_not_an_ai, Jul 15 '22 at 11:29
@AdrianMole, I want to assign this to the result of mmap.find(value); — SPlatten, Jul 15 '22 at 11:29
`auto it = mmap.find(value)` ? Please include the code with the issue in the question — 463035818_is_not_an_ai, Jul 15 '22 at 11:30
You want to use it in a local (member) function, then `auto myIt = mmap.find(value);`. Still not really clear what you want. — Adrian Mole, Jul 15 '22 at 11:30
seems like the issue is this https://stackoverflow.com/questions/1123080/why-do-we-need-typename-here. If you have code that causes a compiler error, you better show the code, see [mcve] — 463035818_is_not_an_ai, Jul 15 '22 at 11:33

score 0 · Answer 1 · answered Jul 15 '22 at 11:29

0

std::map<K, V>::iterator

see member types of std::map

answered Jul 15 '22 at 11:29

Marco Kinski

302
3
7

Tried that before I created this post, won't compile, I get: 'missing 'typename' prior to dependent type name 'std::map::iterator' – SPlatten Jul 15 '22 at 11:31
@SPlatten thats because its a dependent type, you need to add `typename` before. – 463035818_is_not_an_ai Jul 15 '22 at 11:31
@463035818_is_not_a_number, tried, won't compile. – SPlatten Jul 15 '22 at 11:48

Karen Baghdasaryan · Accepted Answer · 2022-07-15T11:52:01.907

0

To avoid confusion with typename keyword. I suggest to do the following

template<typename K, typename V>
class my_map {
private:
    std::map<K, V> mmap;
public:
    typedef typename std::map<K, V>::iterator iterator;
    typedef typename std::map<K, V>::const_iterator const_iterator;

    iterator begin() {return mmap.begin();}
    const_iterator begin() const {return mmap.begin();}
    .
    .
    .
};

You can now use it as my_map<K, V>::iterator or my_map<K, V>::const_iterator.

edited Jul 15 '22 at 11:52

answered Jul 15 '22 at 11:38

Karen Baghdasaryan

2,407
6
24

Still get missing 'typename' prior to dependant type name 'std::map::iterator' and again on the const_iterator. – SPlatten Jul 15 '22 at 11:48
Just edited. Forgot to add the keyword in class. – Karen Baghdasaryan Jul 15 '22 at 11:52

C++ iterator for map derived class

2 Answers2