C structure object member name as parameter - c++

Question

How can I pass a structure name, object name, different member name(whose value to be verified) as a parameter to a function ?
struct st{
int a;
int b;
}
bool verify(____ st , ____ b){
if(obj.b == 5)return true;
return false;
}
int main(){
st obj;
// now that I know all the names of members of struct name
// HOW can I verify passing different member name as parameter
cout<<verify(__,__);
}
For an instance:
(example with error)
#include<iostream>
using namespace std;
struct st{
int a;
int b;
};
bool verify(st obj, st.a val){
if(obj.a==val)
return true;
}
int main()
{
cout<<"Hello World"<<endl;
st obj;
cout<<verify(obj,a);
//cout<<verify(obj,b);
return 0;
}

Answer 1

You can use a pointer to data member:
bool verify(const st &obj, int st::* field) {
return obj.*field == 5;
}
...
st obj;
std::cout << verify(obj, &st::a);
std::cout << verify(obj, &st::b);
But the syntax is confusing and just passing a reference to the data member to verify is easier:
bool verify(int field) {
return field == 5;
}
...
st obj;
std::cout << verify(obj.a);
std::cout << verify(obj.b);
Using a template:
#include <iostream>
struct st
{
int a;
int b;
};
struct st2
{
int c;
int d;
};
template<typename T>
bool verify(const T &obj, int T::* field)
{
return obj.*field == 5;
}
int main()
{
st obj = {5, 6};
st2 obj2 = {5, 6};
std::cout << verify(obj, &st::a) << "\n"; // 1, since obj.a is 5
std::cout << verify(obj2, &st2::d) << "\n"; // 0, since obj.d is not 5
return 0;
}