class 类型的非静态数据成员的声明也是定义吗?

Is a declaration for a non-static data member of a class type also a definition?

我正在学习 C++。特别是声明和定义的区别。据我目前的理解

All definitions are declarations but not all declarations are definitions.

这是我目前所知道的一个例子。

int x; //definition(as well as declaration according to the above quote)
extern int y; //declaration that is not a definition 

class CustomType
{
    int x; //is this a "declaration that is not a definition" OR a "definition"
};
int main()
{
   int p[10]; //definition
   //...
}

我想知道 class' 定义中的 int x; 是不是定义 或 定义的 声明。在标准中的哪个位置说明了这一点,以便我可以阅读更多相关信息。

I want to know whether int x; inside the class' definition is a declaration that is not a definition or a definition.

非静态数据成员的声明(如x定义。