Demonstrate hiding structure layout to public but still allow access.

StructPb.cpp

#include <iostream>
#include <string>

struct PublicData
{
    int a;
    float b;

    // private data
    // this is a technique to hide the struct information thus users won't be able to know its layout
    // although users can still access each member of struct
    struct {
        int c;
        double d;
        std::string e;
    } d;
};

static void PrintInfo(const PublicData& pb)
{
    std::cout << pb.a << "\n" << pb.b << "\n" << pb.d.c << "\n" << pb.d.d << "\n" << pb.d.e << std::endl;
}

int main()
{
    // This initialization is also possible
    PublicData pb {
        1,
        2.5f,
        1,
        2,
        "Test"
    };
    PrintInfo(pb);

    // Maual initialization for each of member variable
    PublicData pb_man;
    pb_man.a = 2;
    pb_man.b = 3;
    pb_man.d.c = 1;
    pb_man.d.d = 2.2f;
    pb_man.d.e = "Test2";
    PrintInfo(pb_man);

    return 0;
}