CODEWITHSUNDEEP
c++
geza
geza

Reputation: 29970

Is static initialization guaranteed here?

Look at this code:

struct Foo {
        void *ptr;

        constexpr Foo() : ptr(nullptr) { }
};

Foo f;

Is it guaranteed that f will be statically initialized?

Clang uses static initialization here, but MSVC doesn't.

Upvotes: 4

Views: 322

Answers (3)

zen-cat
zen-cat

Reputation: 425

I believe it would be also in msvc (at least vs 2015) if you were to declare the f itself as constexpr Foo f;

Upvotes: 0

Dúthomhas
Dúthomhas

Reputation: 10073

Standard-wise, yes. Reality-wise, no.

You are at the mercy of compiler venders when it comes to static initialization compliance.

[edit] Clang is a special compiler — from the beginning its creators have been interested in full standards compliance.

Upvotes: 0

aschepler
aschepler

Reputation: 72431

Yes, the Standard says f will be constant initialized:

[basic.start.init]/2:

A constant initializer for an object o is an expression that is a constant expression, except that it may also invoke constexpr constructors for o and its subobjects even if those objects are of non-literal class types [Note: such a class may have a non-trivial destructor --end note]. Constant initialization is performed:

  • ... [a case for references]

  • if an object with static or thread storage duration is initialized by a constructor call, and if the initialization full-expression is a constant initializer for the object;

  • ... [a case for objects initialized without a constructor call]

Together, zero-initialization and constant initialization are called static initialization; all other initialization is dynamic initialization. Static initialization shall be performed before any dynamic initialization takes place.

The initialization full-expression is simply the call of Foo's default constructor, which is a constant expression.

MSVC is wrong to emit code to initialize f.

Upvotes: 3

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