无法从非原始数据类型的向量中按 ID 删除元素

Question

我有一个用户定义数据类型city 的向量。我试图通过它的 ID 从这个向量中删除一个元素；最终，所有城市都将在while(!cityList.empty()) 循环中从此列表中删除。我打算使用erase-remove 成语来完成此操作。

但是，当我在调用remove() 后制作我的代码时，我收到了一条非常粗糙的错误消息。将 city 对象作为第三个参数传递给 remove() 会导致此错误，传递 city 的 (int) ID 也是如此。 erase() 不会发生此错误，但 remove() 会发生此错误，如果我尝试使用它，find() 也会发生此错误。这是有问题的代码：

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.

错误信息包括“模板参数推导/替换失败”和“'city'不是从'const _gnu_cxx::__normal_iterator<_iteratorl _container>'派生的” 消息，并且我无法在网上找到与我的上述错误问题相关的任何内容。

编辑：我已经修改了我的代码，现在有了：

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);
}

我在尝试编译时收到的错误是：

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)); }
                          ^

这更接近，但我不确定需要什么。但是，main.cpp:30:90 行指向我的 cityList.erase() 函数的 cityList[i] == cityToRemove 部分，所以我知道问题出在我的比较表达式中。

我的演示也更新了。

Answer 1

你需要定义一个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;
}

还可以调用erase，如example here。