std :: map查找无法正常工作

Question

std::map.find() is intended to return an map::iterator to an element it found if there is some or to the end() if not. I get BadPtr returned to me. The exactly same construct works fine in the other part of code. What is this?

class OntologyContainer {
    map<string, OntologyClass*> data;
    OntologyClass* last_added;
public:
    class iterator : public std::iterator<bidirectional_iterator_tag, OntologyClass> {
        map<string, OntologyClass*>::iterator itr;
    public:
        iterator(map<string, OntologyClass*>::iterator it) : itr(it) { }

    ...
    }

    iterator begin() {
        return iterator(data.begin());
    }

    iterator end() {
        return iterator(data.end());
    }

    iterator Find(const string & to_find) {
        map<string, OntologyClass*>::iterator it = data.find(to_find);
        // this is where it fails
        return iterator(it);
    }

map::iterator is wrapped for the sake of making operators * and -> returning OntologyClass objects and pointers respectively:

            OntologyClass& operator* () {
        return *(itr->second);
    }

    OntologyClass* operator->() {
        return itr->second;
    }

Answer 1

It might be something to do with the fact that you inherit from std::iterator<bidirectional_iterator_tag, OntologyClass> , making your iterator value_type to be OntologyClass , rather than a pointer to OntologyClass , which is what your map iterator uses. How are you implementing the dereference operator?

Answer 2

if you can use boost I suggest using boost::transform_iterator.

This stack overflow answer has a decent example on how to do that: iterator adapter to iterate just the values in a map?