Value initialize aggregate

Question

Tried C++ standard, but couldn't figure it out. Are these equivalent?

double x[2] = {0.0, 0.0};

and

double x[2] = {};

How about these?

struct A {
    double x[2];
};

A a = {0.0, 0.0};

and

A a = {};

Thank you!

C or C++? You've tagged the question with both. – CB Bailey Jun 22 '11 at 07:50 — CB Bailey, Jun 22 '11 at 07:50
It's supposed to be `A a = { {0.0, 0.0} };` – littleadv Jun 22 '11 at 07:52 — littleadv, Jun 22 '11 at 07:52

Oliver Charlesworth · Accepted Answer · 2011-06-22T07:58:36.737

4

The C++ standard says (8.5.1):

If there are fewer initializers in the list than there are members in the aggregate, then each member not explicitly initialized shall be value-initialized

and value-initialization of a double is to set it to 0.0.

So yes! In C++ they are equivalent.

[I haven't had time to check the C99 standard.]

edited Jun 22 '11 at 07:58

answered Jun 22 '11 at 07:50

Oliver Charlesworth

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score 3 · Answer 2 · answered Jun 22 '11 at 07:49

3

Yes, they are.

Compiler fills the initialization with zeroes when not enough given per declared size.

answered Jun 22 '11 at 07:49

littleadv

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Value initialize aggregate

2 Answers2