c++ - 这里保证静态初始化吗？

Question

看这段代码:

struct Foo {
        void *ptr;

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

Foo f;

是否保证f会被静态初始化？

Clang 在这里使用静态初始化，但是 MSVC doesn't .

Answer 1

是的，标准说 f 将被常量初始化:

[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.

初始化全表达式只是调用Foo的默认构造函数，它是一个常量表达式。

MSVC 发出初始化 f 的代码是错误的。