"Expression must have class type" when calling simple inherited method

Question

Do you guys have any hint what's wrong with my code? I've made it as simple as possible and tried to search all over google but still have no idea.

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;

class Animal {
public:
    Animal();
    Animal(string _sound) :
        sound(_sound) {}
    virtual ~Animal();
    void give_sound() {
        cout << sound << " ";
    }
protected:
    string sound;
};

class Dog : protected Animal {
public:
    Dog(): Animal("woof") {}
};

int main() {

    Dog doggy();
    doggy.give_sound(); // expression must have class type

    return 0;
}

Everything fixed up [here](http://coliru.stacked-crooked.com/a/0be113f40bce9bd6). — πάντα ῥεῖ, Nov 15 '16 at 21:58

StoryTeller - Unslander Monica · Answer 1 · 2016-11-15T21:53:40.227

6

Believe it or not Dog doggy(); declares a function names doggy. It returns a Dog by value, and accepts no parameters.

To amend it, don't use parenthesis (if you don't have any parameters to pas) when defining objects with auto storage. Just do Dog doggy;. Alternatively, you can do it in c++11 and onward as Dog doggy{};

edited Nov 15 '16 at 21:53

answered Nov 15 '16 at 21:50

StoryTeller - Unslander Monica

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also if he inherits using protected he wont be able to call give_sound() as it wont be accessible. He needs public inheritance – Adrian Lis Nov 15 '16 at 21:52
what the heck? not an instance of Dog? I'm begginer to c++ and its inheritance mechanisms but now I'm even more confused. How can I fix it? – IFeel3 Nov 15 '16 at 21:52
@IFeel3, I told you, remove the parenthesis (unless you need to pass parameters). – StoryTeller - Unslander Monica Nov 15 '16 at 21:53
@IFeel3 It's called the [most vexing parse](https://en.wikipedia.org/wiki/Most_vexing_parse). `doggy` is a function that takes no arguments and returns `Dog`. – Justin Time - Reinstate Monica Nov 15 '16 at 21:55
@StoryTeller Thank you. I'm used to Java and I thought that initializing without parenthesis makes an empty object without properly initialized fields. – IFeel3 Nov 15 '16 at 21:57
1

@IFeel3, that's an honest mistake. But constructors for objects are always called whenever you define a variable. – StoryTeller - Unslander Monica Nov 15 '16 at 21:57
hi, can i ask, Dog doggy(); style is allowed in my compiler im using gcc 4.9.2 – Lorence Hernandez Nov 15 '16 at 23:43
@LorenceHernandez, that may very well be either a compiler extension or bug, since according to the standard, it's a function declaration. I lean towards bug, because [gcc 5.1 emits an error](https://godbolt.org/g/4q2h2V) – StoryTeller - Unslander Monica Nov 16 '16 at 06:30
@StoryTeller thanks for that. – Lorence Hernandez Nov 16 '16 at 06:55

"Expression must have class type" when calling simple inherited method

1 Answers1