Brace initialization for class with virtual function

Question

There is this code:

struct A {
   int x;
   void f() {}
};

struct B {
   int y;
   virtual void f() {}
};

A a = {2};

//B b = {3}; error: no matching constructor for initialization of 'B'

int main() {
   return 0;
}

Why initialization for variable a works but not for variable b?

Brace initialization only works for POD types; making your method virtual makes it non-POD — antlersoft, May 16 '13 at 19:25
[What are Aggregates and Pods and how/why they are special](http://stackoverflow.com/questions/4178175/what-are-aggregates-and-pods-and-how-why-are-they-special) — Armen Tsirunyan, May 16 '13 at 19:40

score 12 · Accepted Answer · answered May 16 '13 at 19:25

12

A is an aggregate, and so can have brace initialization, and B isn't, since it has a virtual method.

8.5.1 Aggregates

An aggregate is an array or a class (Clause 9) with no user-provided constructors (12.1), no brace-or-equal- initializers for non-static data members (9.2), no private or protected non-static data members (Clause 11), no base classes (Clause 10), and no virtual functions (10.3).

answered May 16 '13 at 19:25

juanchopanza

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The answer is right, but there is no need to qualify with the '11 standard, as the answer is exactly the same in C++98, C++03 and C++11 – David Rodríguez - dribeas May 16 '13 at 19:28
@DavidRodríguez-dribeas Thanks again. I wasn't sure if this was phrased in terms of aggregate or POD in C++03. – juanchopanza May 16 '13 at 19:29
1

couldn't you write a brace initializer constructor however? taking an initializer list as an arg? – Syntactic Fructose May 16 '13 at 19:45
@DavidRodriguez Wouldn't uniform initialization in C++11 that uses braces be called "brace-initialization"? – Yakk - Adam Nevraumont May 16 '13 at 19:46
@Need4Sleep yes you could, in C++11. – juanchopanza May 16 '13 at 19:47
@Need4Sleep also, adding a constructor taking a single `int` would allow for the same initialization syntax. – juanchopanza May 16 '13 at 19:54

Brace initialization for class with virtual function

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