How to erase a certain element from a shared_ptr to a vector of objects? - c++

Question

I have created a member variable (in the class Group) that is a shared_ptr to a vector (called members that stores objects of type User (a different class). Here is the member variable definition (empty):
std::shared_ptr <std::vector<User>> members = std::make_shared<std::vector<User>>();
To eliminate a certain User object from the vector (members), I created a member function (remove) inside the class Group. It checks all the User objects inside the vector and, when encounters the one with the a.URI value that is looking for, it erases the object at that location in the vector.
void Group::remove(User a) {
for (auto i = 0; i < members->size(); i++){
if (a.URI == (*(members->begin()+i)).URI) members->erase(*(members->begin() + i));
}
That is my remove function by now, but it doesn't work. I have checked different configurations but can`t make it work. Is there a problem with my function? How should this function be implemented (special rules for shared_ptr?)? Is there a better/optimal way?
I think no more code is needed here to solve my question. However, for those who want a MCV example, I tried to write one here (Ideone).

Answer 1

Firstly, std::vector::erase expects an iterator as its argument, so change
members->erase(*(members->begin() + i))
to
members->erase(members->begin() + i)
Secondly, after the element being erased, when i++ is evaluated, you will skip the next element or get out of the bound of the vector. You might change the loop to
for (auto i = 0; i < members->size(); ) {
if (a.URI == (*(members->begin()+i)).URI)
members->erase(members->begin() + i);
else
i++;
}

Answer 2

Why don't you declare the vector members as static member of the group class. I did it like this:
#include <bits/stdc++.h>
using namespace std;
class User{
public:
int URI;
User(int a){
URI = a;
}
};
class Group {
public:
static vector<User> members;
void remove(User a) {
for (int i = 0; i < members.size();){
if (a.URI == (*(members.begin()+i)).URI) members.erase((members.begin() + i));
else
i++;
}
}
Group(User a, User b, User c){
members.push_back(a);
members.push_back(b);
members.push_back(c);
}
};
vector<User> Group::members;
int main() {
User a(1), b(2), c(3);
Group obj(a, b, c);
obj.remove(a);
return 0;
}
Hope it helps.