struct in class

Question

I have struct in class and not know how to call variables from struct, please help ;)

#include 
using namespace std;

class E
{
public: 
            


        

Answer 1

I'd like to add another use case for an internal struct/class and its usability. An inner struct is often used to declare a data only member of a class that packs together relevant information and as such we can enclose it all in a struct instead of loose data members lying around.

The inner struct/class is but a data only compartment, ie it has no functions (except maybe constructors).

#include 

class E
{
    // E functions..
public:
    struct X
    {
        int v;
        // X variables..
    } x;
    // E variables..
};

int main()
{
    E e;
    e.x.v = 9;
    std::cout << e.x.v << '\n';
    
    E e2{5};
    std::cout << e2.x.v << '\n';

    // You can instantiate an X outside E like so:
    //E::X xOut{24};
    //std::cout << xOut.v << '\n';
    // But you shouldn't want to in this scenario.
    // X is only a data member (containing other data members)
    // for use only inside the internal operations of E
    // just like the other E's data members
}

This practice is widely used in graphics, where the inner struct will be sent as a Constant Buffer to HLSL. But I find it neat and useful in many cases.