What are Aggregates and PODs in C++?

POD is an acronym in C++ that means plain old data. It is a class/struct that ONLY has member variables and no methods, constructors, destructors, virtual functions, etc. For example,

Example

#include<iostream>
using namespace std;

// POD
struct MyStruct {
   int key;
   string data;
};
int main() {
   struct MyStruct s;
   s.key = 1;
   s.data = "hello";
   return 0;
}

The struct MyStruct has no user defined ctor, dtor, etc and hence is a POD.

An aggregate is an array or a class with no user-declared constructors, no private or protected non-static data members, no base classes, and no virtual functions.

An aggregate class is called a POD if it has no user-defined copy-assignment operator and destructor and none of its non-static members is a non-POD class, array of non-POD, or a reference.