是。

不幸的是下面的措词来自今天的标准草案，但是原理在C ++ 11中是相同的。

Unfortunately the wording below is from the standard draft as of today, but the principle is the same in C++11.

[class.default.ctor] / 4 一个默认构造函数，默认为默认值，未定义为Delete，当它为 odr用过的（ [basic.def.odr] ）创建其类类型的对象（ [intro.object] ），需要进行常量评估（ [expr.const] ），或者在首次声明后明确将其默认为默认值。 隐式定义的默认构造函数执行该类的初始化集，该初始化集由该类的用户编写的默认构造函数执行，而没有 ctor-initializer （ [class.base.init] ）和一个空的复合语句。

[class.default.ctor]/4 A default constructor that is defaulted and not defined as deleted is implicitly defined when it is odr-used ([basic.def.odr]) to create an object of its class type ([intro.object]), when it is needed for constant evaluation ([expr.const]), or when it is explicitly defaulted after its first declaration. The implicitly-defined default constructor performs the set of initializations of the class that would be performed by a user-written default constructor for that class with no ctor-initializer ([class.base.init]) and an empty compound-statement.

[class.base.init] / 9 在非委托构造函数中，如果给定的潜在构造子对象未由 mem-initializer-id 指定（包括没有 mem-initializer的情况-list ，因为构造函数没有 ctor-initializer ），则：

[class.base.init]/9 In a non-delegating constructor, if a given potentially constructed subobject is not designated by a mem-initializer-id (including the case where there is no mem-initializer-list because the constructor has no ctor-initializer), then:

1. 如果实体是具有默认成员初始值设定项（ [class.mem] ）和
   

1. 的非静态数据成员构造函数的类是联合（ [class.union] ），并且该联合的其他任何变体成员都没有由 mem-initia指定lizer-id 或


2. 构造函数的类不是联合体，并且，如果实体是匿名联合体的成员，则该联合体的其他成员都不会由 mem-initializer-id ，实体是根据 [dcl.init] 中指定的默认成员初始化程序进行初始化的;

1. the constructor's class is a union ([class.union]), and no other variant member of that union is designated by a mem-initializer-id or
2. the constructor's class is not a union, and, if the entity is a member of an anonymous union, no other member of that union is designated by a mem-initializer-id, the entity is initialized from its default member initializer as specified in [dcl.init];

[..]

简而言之，我想知道默认构造函数是否保证将设置默认成员值。

In short, I'm wondering if the default constructor guarantees that default member values will be set.

确切的示例紧随上面引用的段落。

An example of exactly this follows the passage latterly quoted above.

但是，如果要定义 A :: A（）并为 x ，它将优先于内联初始化程序。

However, if you were to define A::A() and provide an initialiser for x, it would take precedence over the inline initialiser.