C++ multiple inheritance function call ambiguity

Question

I have a basic question related to multiple inheritance in C++. If I have a code as shown below:

struct base1 {
   void start() { cout << "Inside base1"; }
};

struct base2 {
   void start() { cout << "Inside base2"; }
};

struct derived : base1, base2 { };

int main() {
  derived a;
  a.start();
}

which gives the following compilation error:

1>c:\mytest.cpp(41): error C2385: ambiguous access of 'start'
1>      could be the 'start' in base 'base1'
1>      or could be the 'start' in base 'base2'

Is there no way to be able to call function start() from a specific base class using a derived class object?

I don't know the use-case right now but.. still!

Similar to http://stackoverflow.com/questions/4831759/ambiguous-definition-of-operator-with-multiple-inheritance — Ioan Paul Pirau, Jul 27 '11 at 14:22
@JohnPaul not the same though; this one is about two base classes with an identical function, that one is about two base classes that have a function with the same name, but differing arguments. — dascandy, Jul 27 '11 at 20:33

score 96 · Accepted Answer · answered Jul 27 '11 at 14:12

96

a.base1::start();

a.base2::start();

or if you want to use one specifically

class derived:public base1,public base2
{
public:
    using base1::start;
};

answered Jul 27 '11 at 14:12

dascandy

7,184
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score 4 · Answer 2 · answered Jul 27 '11 at 14:11

4

Sure!

a.base1::start();

or

a.base2::start();

answered Jul 27 '11 at 14:11

Lightness Races in Orbit

378,754
76
643
1,055

Trying to understand - "if the inheritance were virtual, there would be no ambiguity". How is that? – goldenmean Jul 27 '11 at 14:19
@goldenmean: That hasn't been part of my answer for a while now. – Lightness Races in Orbit Jul 27 '11 at 14:22

user3742309 · Answer 3 · 2021-01-12T12:10:22.517

2

In addition to the answers above, if we are in the case of NON-VIRTUAL inheritance:

you can:

use static_cast<base1*>(a).start()

or

override start() in derived

Btw - please note the diamond problem that can appear. In this case you might want to use virtual.

edited Jan 12 '21 at 12:10

answered Jan 12 '21 at 12:01

user3742309

183
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C++ multiple inheritance function call ambiguity

3 Answers3

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