什么是 C++ 中的标量对象? [英] What is a scalar Object in C++?

问题描述

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

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?

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

推荐答案

简短版本: C++ 中的类型是:

Short version: Types in C++ are:

• 对象类型:标量、数组、类、联合

• Object types: scalars, arrays, classes, unions

引用类型

函数类型

(成员类型)[见下文]

(Member types) [see below]

void

长版

• 对象类型

• Object types

• 标量

1. 算术(整数、浮点数)

1. arithmetic (integral, float)

指针:T * 用于任何类型 T

pointers: T * for any type T

枚举

成员指针

nullptr_t

数组:T[] 或 T[N] 用于任何完整的非引用类型 T

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

类:class Foo 或 struct Bar

1. 琐碎的课程

1. Trivial classes

聚合

POD 类

(等等等等)

联合:联合邮编

引用类型:T &、T && 用于任何对象或自由函数类型T

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

函数类型

• 自由函数:R foo(Arg1, Arg2, ...)

成员函数:R T::foo(Arg1, Arg2, ...)

void

成员类型是这样工作的.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.您只能拥有成员指针.成员指针具有类型 T::* U，如果 U 是(自由)对象类型，则它是指向成员对象的指针，并且指针-如果 U 是(自由)函数类型，则为成员函数.

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 U is a (free) object type, and a pointer-to-member-function if U is a (free) function type.

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

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

所有类型都可以const/volatile限定.

All types can be const/volatile qualified.

标头提供了 trait 类来检查这些类型特征中的每一个.

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

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