CODEWITHSUNDEEP
c++reference
jeffreyveon
jeffreyveon

Reputation: 13840

C++ - default initialisation of a reference member - how does this even work?

Default initialization of a reference variable generates an error in GCC 4.8, but the following seems to compile and work without any warning/error.

struct Foo {
    int &bar;

    Foo(): bar(bar) { }
};

int main () {
  Foo foo;
  cout << foo.bar;  // prints 0
  return 0;
}

How does this compile? I'm particularly perplexed by this line:

Foo(): bar(bar) { }

Upvotes: 3

Views: 75

Answers (1)

Mike Seymour
Mike Seymour

Reputation: 254751

It doesn't work, it's undefined behaviour.

It compiles because you can, in general, refer to a variable in its initialiser. This can have valid uses:

void * p = &p;

but in most cases leads to UB. You should get a warning about using an uninitialised value, if you enable sufficent warnings. In GCC, -Wuninitialized (or -Wall) should do it.

Upvotes: 4

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