Question

I am attempting to print out all of the elements in each vector from a multiset of vectors. The build is failing but the error is occurring somewhere in a header file, I’m afraid I don’t really understand the error codes at all. Any help would be greatly appreciated! Here is the error:

error: invalid conversion from 'const std::basic_string<char, std::char_traits<char>, std::allocator<char> >* const' to 'std::basic_string<char, std::char_traits<char>, std::allocator<char> >*'

And here is the code causing the problems.

multiset<vector < string > > setOfRules;
vector<string> testing,testing2;

testing.push_back("bar");
testing.push_back("foo");
testing2.push_back("foo2");
testing2.push_back("bar2");
setOfRules.insert(testing);
setOfRules.insert(testing2);

for (multiset< vector <string > >::iterator myIterator = setOfRules.begin();
     myIterator!=setOfRules.end(); 
     ++myIterator) 
{

    for (vector< string >::iterator myOtherIterator = ( *myIterator ).begin(); 
         myOtherIterator != ( *myIterator ).end(); 
         ++myOtherIterator) 
    {
        cout << *myOtherIterator << " " ;
    }
    cout << endl;
}

Answer 1

C++11 Standard claims that for associative containers where the value type is the same as the key type, both iterator and const_iterator are constant iterators.

So actually multiset<vector<string>>::iterator is const_iterator. The same trick with std::set iterators – they are all consts.

This means that vector<string>::iterator myOtherIterator = *myIterator.begin() statement will fail because you try obtain non-const iterator from const object (given by *myIterator which is const).

To fix you need to use vector<string>::const_iterator:

for(multiset<vector<string>>::const_iterator myIterator = setOfRules.begin(); 
    myIterator != setOfRules.end(); ++myIterator)
{
   for(vector<string>::const_iterator myOtherIterator = *myIterator.begin();     
      myOtherIterator != *myIterator.end(); ++myOtherIterator)
   {
      cout << *myOtherIterator << " ";
   }
   cout << endl;
}