Can't remove element by ID from vector of non primitive datatypes

Question

I have a vector of my user-defined data type city. I'm trying to remove an element from this vector by its ID; eventually all cities will be removed from this list in a while(!cityList.empty()) loop. I plan to use the erase-remove idiom to accomplish this.

However, I'm getting a very gnarly error message when I make my code after calling remove(). Passing in the city object as the third parameter to remove() results in this error, as does passing in the (int) ID of the city. This error doesn't occur with erase(), but does with remove(), and also find() if I try to use that. Here is the code in question:

vector<city> cityList;
cityList.push_back(city(1));
cityList.push_back(city(2));
cityList.push_back(city(3));

city cityToRemove = cityList[0];
int idOfCityToRemove = cityList[0].getID();

remove(cityList.begin(), cityList.end(), cityToRemove);
//remove(cityList.begin(), cityList.end(), idOfCityToRemove);

Here is an updated simple, minimal demo of my problem.

The error message includes "template argument deduction/substitution failed" and "‘city’ is not derived from ‘const _gnu_cxx::__normal_iterator<_IteratorL, _Container>’ " messages, and I haven't been able to find anything online relating to my problem with the above errors.

Edit: I've modified my code such that I now have:

int main(int argc, char** argv) {

vector<city> cityList;
cityList.push_back(city(1));
cityList.push_back(city(2));
cityList.push_back(city(3));

city cityToRemove = cityList[0];
int idOfCityToRemove = cityList[0].getID();
int i;

for (i = 0; i < cityList.size(); i++) {
    cityList.erase(remove_if(cityList.begin(), cityList.end(),  cityList[i] == cityToRemove), cityList.end());
}
//remove(cityList.begin(), cityList.end(), cityToRemove);
//remove(cityList.begin(), cityList.end(), idOfCityToRemove);

return 0;
}

bool operator ==(const city &a, const city &b)
{
    return (a.id == b.id);
}

and the error I receive when attempting to compile is:

In file included from /usr/include/c++/5/bits/stl_algobase.h:71:0,
             from /usr/include/c++/5/bits/char_traits.h:39,
             from /usr/include/c++/5/ios:40,
             from /usr/include/c++/5/ostream:38,
             from /usr/include/c++/5/iostream:39,
             from main.cpp:2:
/usr/include/c++/5/bits/predefined_ops.h: In instantiation of ‘bool __gnu_cxx::__ops::_Iter_pred<_Predicate>::operator()(_Iterator) [with _Iterator = __gnu_cxx::__normal_iterator<city*, std::vector<city> >; _Predicate = bool]’:
/usr/include/c++/5/bits/stl_algo.h:866:20:   required from _ForwardIterator std::__remove_if(_ForwardIterator, _ForwardIterator, _Predicate) [with _ForwardIterator = __gnu_cxx::__normal_iterator<city*, std::vector<city> >; _Predicate = __gnu_cxx::__ops::_Iter_pred<bool>]’
/usr/include/c++/5/bits/stl_algo.h:936:30:   required from ‘_FIter std::remove_if(_FIter, _FIter, _Predicate) [with _FIter = __gnu_cxx::__normal_iterator<city*, std::vector<city> >; _Predicate = bool]’
main.cpp:30:90:   required from here
/usr/include/c++/5/bits/predefined_ops.h:234:30: error: expression cannot be used as a function
{ return bool(_M_pred(*__it)); }
                          ^

This is closer, but I'm not sure what is required. The line main.cpp:30:90 points to the cityList[i] == cityToRemove part of my cityList.erase() function, however, so I know that the issue is within my comparison expression.

My demo is also updated.

Please **[edit]** your question with a [mcve] or [SSCCE (Short, Self Contained, Correct Example)](http://sscce.org) — NathanOliver, Sep 23 '16 at 18:17
It's much preferred to put your code in your post, rather than linking to an external site. — smead, Sep 23 '16 at 18:21
It's now edited to include code in the post as well as the minimal example. — Jthami05, Sep 23 '16 at 18:25
@Jthami05: "minimal, complete" means that it needs to be possible to copy and paste the code from your question, and it compile. — Steve Jessop, Sep 23 '16 at 18:26
You probably want `std::remove_if`, together with a predicate for testing whether a city has a given ID. — isekaijin, Sep 23 '16 at 18:28

score 0 · Answer 1 · answered Sep 23 '16 at 18:44

0

You need to define an operator ==:

class city {
    public:
        city(int idin);
        int getID();

    private:
        int id;

    friend bool operator==(const city &a, const city &b);
};

.

bool operator ==(const city &a, const city &b)
{
    return a.id == b.id;
}

and also call erase as in the example here.

answered Sep 23 '16 at 18:44

smead

1,768
15
23

Adding the operator overloading function to my class and calling it in main.cpp with a for loop as `cityList.erase(remove_if(cityList.begin(), cityList.end(), cityList[i] == cityToRemove), cityList.end());` decreasese the number of errors, but I still get the "required from ‘_ForwardIterator" error and am unable to compile. – Jthami05 Sep 23 '16 at 19:11
Post the new code, then? And the full error message. – smead Sep 23 '16 at 19:26

Can't remove element by ID from vector of non primitive datatypes

1 Answers1