How to compare two objects using templates? - c++

Question

I want to compare two objects and get larger among them using templates. Passing the object as an argument isn't working as the code below. See the sample code given below. That's what I'm trying to do.
#include <iostream>
using namespace std;
template <class T>
class max
{
T a;
public:
max(T a)
{
this.a = a;
}
T Large(T n2)
{
return (a > n2.a) ? a : n2.a;
}
};
int main()
{
max <int> obj1(10);
max <int> obj2(20);
cout<<obj1.Large(obj2)<<" is larger"<<endl;
return 0;
}
I'm doing something like this but by comparing 2 objects.
// class templates
#include <iostream>
using namespace std;
template <class T>
class mypair {
T a, b;
public:
mypair (T first, T second)
{a=first; b=second;}
T getmax ();
};
template <class T>
T mypair<T>::getmax ()
{
T retval;
retval = a>b? a : b;
return retval;
}
int main () {
mypair <int> myobject (100, 75);
cout << myobject.getmax();
return 0;
}

Answer 1

This code seems to work fine, let me know if this helps
#include <iostream>
using namespace std;
template <class T>
class Maxi {
T a;
public:
Maxi(T val)
{
this->a = val;
}
T Large(maxi n2)
{
return (a > n2.a) ? a : n2.a;
}
};
int main() {
Maxi <int> obj_1(10);
Maxi <int> obj_2(20);
cout<<obj_1.Large(obj_2)<<" is larger"<<endl;
return 0;
}

Answer 2

There is already a max and min template function provided under algorithm.
Just call std::max(10, 20) to get the larger between the two.
You can even provide your own comparator for custom comparison.
Side note: It seems like by including iostream, you can use max and min without algorithm.

Answer 3

Problems I see:
Use of
using namespace std;
is probably going to mess things up for you since std::max gets pulled into the mix indirectly. It does for me with g++. Don't use it.
Syntax error in the following line:
this.a = a;
That needs to be
this->a = a;
Argument to Large needs to be of type max, not T.
For good measure, I would also make it a const member function.
T Large(max n2) const
{
return (a > n2.a) ? a : n2.a;
}
Use std::cout and std::endl since using namespace std; is problematic.
Here's an updated version of your code with the above fixes:
#include <iostream>
template <class T>
class max
{
private:
T a;
public:
max(T a)
{
this->a = a;
}
T Large(max n2) const
{
return (a > n2.a) ? a : n2.a;
}
};
int main()
{
max <int> obj1(10);
max <int> obj2(20);
std::cout << obj1.Large(obj2) << " is larger"<<std::endl;
return 0;
}
It works for me and produces the following output:
20 is larger

Answer 4

I think you're trying to do this:
template <typename T>
T max(const T &a, const T &b)
{ return (b < a) ? a : b; }
That's how you do that. Your weird mishmash of a class doesn't make any sense at all. And so if I got what you're trying to do wrong, please explain yourself better.
Templates don't have to be classes you know. You can have templated functions.
If you absolutely must use a class, do this then:
template <typename T>
class max
{
T operator ()(const T &a, const T &b) { return (b < a) ? a : b; }
};
int main()
{
max<int> foo;
cout << foo(10, 20) << " is larger\n"; // Don't use endl most of the time.
return 0;
}
Suppose you have two objects that aren't ints, what do you do? Well, you do this:
#include <iostream>
#include <algorithm>
struct A {
int v1;
int v2;
};
bool operator <(A &a, A &b)
{
return (a.v1 < b.v1) || ((a.v1 == b.v1) && (a.v2 < b.v2));
}
::std::ostream &operator <<(::std::ostream &os, const A &a)
{
os << "{" << a.v1 << ", " << a.v2 << "}";
}
int main()
{
A first{10, 20};
B second{20, 10};
::std::cout << ::std::max(first, second) << " is the larger.\n";
}
If you don't want to have to define operator <, then do this:
bool my_less_than(const A &a, const A &b)
{
return (a.v1 < b.v1) || ((a.v1 == b.v1) && (a.v2 < b.v2));
}
int main()
{
A first{10, 20};
B second{20, 10};
::std::cout << ::std::max(first, second, my_less_than) << " is the larger.\n";
}