How to access member function with iterator in C++ std::set - c++

Question

I am trying to iterate over a C++ std::set and access a member function. But my following code is not working.
#include <iostream>
#include <set>
using namespace std;
class A;
std::set<A> m_vector;
std::set<A>::iterator iter = m_vector.begin();
class A
{
public:
int age;
A()
{
cout << "enter age" << endl;
cin >> age;
}
int getAge()
{
return age;
}
private:
};
void addNewVoter()
{
m_vector.insert(A());
}
int main()
{
addNewVoter();
addNewVoter();
addNewVoter();
for (size_t i = 0; i < m_vector.size(); i++)
{
cout << (*iter)->getAge(); /* Here is the mistake. I can't invoke this.*/
iter++;
}
}
My question is, how can I invoke member function with iterator?

Answer 1

Initialize iter when you are ready to traverse. Also, access member(s) by either iter->getAge() or (*iter).getAge().
#include <iostream>
#include <set>
using namespace std;
class A;
std::set<A> m_vector;
std::set<A>::iterator iter;
/* other codes */
int main()
{
addNewVoter();
addNewVoter();
addNewVoter();
iter = m_vector.begin();
while( iter != m_vector.end() )
{
cout << iter->getAge();
iter++;
}
}

Answer 2

Three changes are required in your code snippet. std::set internally implementing a red black binary tree and it required an operator overloading for comparison.
So you class should have an additional function:
bool operator <(const A& other) const
{
return age < other.age;
}
Then while you call getAge() function system passing a const object of A, so your getAge function should be a const function.
int getAge() const
^^^^^
{
return age;
}
Third one, you should invoke the getAge function either using one of these syntax. (*iter).getAge() or iter->getAge(); dont mix it up.
Demo

Answer 3

Edit first:
Let's say you at least know how to invoke that member function through pointer. The answer is iter->getAge() or (*iter).getAge() - in the comments.
Then you're doing this:
std::set<A> my_set;
auto it = my_set.begin();
// some inserts
std::cout << it->getAge() << std::endl;
which is undefined behaviour. You don't dereference begin iterator acquired originally from an empty container.
Just use this, instead:
for (auto it = my_set.begin(); it != my_set.end(); ++it)
std::cout << it->getAge() << std::endl;
or the range-based for...
As you can see, I refused to use your naming conventions because they're bad and misleading.