什么是 C++ 中的标量对象？

What is a scalar Object in C++?

提问by odinthenerd

As far as I understand it fundamental types are Scalar and Arrays are aggregate but what about user defined types? By what criteria would I divide them into the two categories?

据我了解，基本类型是标量，数组是聚合的，但是用户定义的类型呢？我会根据什么标准将它们分为两类？

struct S { int i; int j };
class C { public: S s1_; S s2_ };
std::vector<int> V;
std::vector<int> *pV = &v;

回答by Kerrek SB

Short version:Types in C++ are:

简短版本：C++ 中的类型是：

• Object types: scalars, arrays, classes, unions

• Reference types

• Function types

• (Member types) [see below]

• void

• 对象类型：标量、数组、类、联合

• 引用类型

• 函数类型

• （成员类型）[见下文]

• void

---

---

Long version

长版

• Object types

  • Scalars

    1. arithmetic (integral, float)

    2. pointers: T *for any type T

    3. enum

    4. pointer-to-member

    5. nullptr_t

  • Arrays: T[]or T[N]for any complete, non-reference type T

  • Classes: class Fooor struct Bar

    1. Trivial classes

    2. Aggregates

    3. POD classes

    4. (etc. etc.)

  • Unions: union Zip

• References types: T &, T &&for any object or free-function type T

• Function types

  • Free functions: R foo(Arg1, Arg2, ...)

  • Member functions: R T::foo(Arg1, Arg2, ...)

• void

• 对象类型

  • 标量

    1. 算术（整数，浮点数）

    2. 指针：T *对于任何类型T

    3. 枚举

    4. 指向成员的指针

    5. nullptr_t

  • 数组：T[]或T[N]任何完整的非引用类型T

  • 班级：class Foo或struct Bar

    1. 琐碎类

    2. 聚合体

    3. POD类

    4. （等等等等）

  • 工会： union Zip

• 引用类型：T &,T &&用于任何对象或自由函数类型T

• 函数类型

  • 免费功能： R foo(Arg1, Arg2, ...)

  • 会员功能： R T::foo(Arg1, Arg2, ...)

• void

Member types work like this. A member type is of the form T::U, but you can't have objects or variables of member type. You can only have member pointers. A member pointer has type T::* U, and it is a pointer-to-member-object if Uis a (free) object type, and a pointer-to-member-function if Uis a (free) function type.

成员类型的工作方式是这样的。成员类型的形式为T::U，但您不能拥有成员类型的对象或变量。你只能有成员指针。成员指针具有 type T::* U，如果U是（自由）对象类型，则它是指向成员对象的指针，如果U是（自由）函数类型，则是指向成员函数的指针。

All types are complete except void, unsized arrays and declared-but-not-defined classes and unions. All incomplete types except voidcan be completed.

除了void、未定义大小的数组和声明但未定义的类和联合之外，所有类型都是完整的。除了void可以完成的所有不完整类型。

All types can be const/volatilequalified.

所有类型都可以const/volatile限定。

The <type_traits>header provides trait classes to check for each of these type characteristics.

所述<type_traits>头部提供性状类来检查每个这些类型的特征。

回答by v.oddou

I think this would be a more comprehensive answer:

我认为这将是一个更全面的答案：

original document:
http://howardhinnant.github.io/TypeHiearchy.pdf

原始文档：http:
//howardhinnant.github.io/TypeHiearchy.pdf

a scalar is a fundamental except it cannot be void, but it can be a pointer type, or an enum type.

标量是基本的，但它不能为空，但它可以是指针类型或枚举类型。

And a fundamental has a keyword in the language. it is easy to recognize when said like that.

并且一个基本语言中有一个关键字。这样说时很容易识别。

回答by Jaege

There is a series of library classes that used for test the type of variables. std::is_scalarcan be used to test if an object is a scalar.

有一系列用于测试变量类型的库类。 std::is_scalar可用于测试对象是否为标量。

A scalar typeis a type that has built-in functionality for the addition operator without overloads (arithmetic, pointer, member pointer, enum and std::nullptr_t).

甲标量类型是已经内置功能的加法运算符不重载（算术，指针，指针构件，枚举和类型std::nullptr_t）。

Also a table from here.

还有一张来自这里的桌子。