Return a “NULL” object if search result not found

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In C++, references can’t be null. If you want to optionally return null if nothing is found, you need to return a pointer, not a reference:

Attr *getAttribute(const string& attribute_name) const {
   //search collection
   //if found at i
        return &attributes[i];
   //if not found
        return nullptr;
}

Otherwise, if you insist on returning by reference, then you should throw an exception if the attribute isn’t found.

(By the way, I’m a little worried about your method being const and returning a non-const attribute. For philosophical reasons, I’d suggest returning const Attr *. If you also may want to modify this attribute, you can overload with a non-const method returning a non-const attribute as well.)

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