Simple Example

#include <iostream>
#include <vector>

using namespace std;

struct Base {
    int av;
};

struct A : public Base {
    int bv;
};

struct database {
    vector <Base> basev;
    Base NBase;

    database () { NBase.av = 0; }

    Base& findb (int value) {
        for (int i = 0; i < basev.size (); ++i) {
            if (basev [i].av == value) return basev [i];
        }
        return NBase;
    }

} db;


int main( ) {

    Base der;
    der.av = 5;
    db.basev.push_back (der);

    Base found = db.findb (5);

    cout << found.av << endl;
}