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13 D语言 结构 联合Structs & Unions

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by: uFramer D语言论坛 http://www.d-programming-language-china.org
from: http://www.digitalmars.com/d/struct.html
version: 基于D 1.013 (Apr 19, 2007)

Whereas classes are reference types, structs are value types. Any C struct can be exactly represented as a D struct. In C++ parlance, a D struct is a POD (Plain Old Data) type, with a trivial constructors and destructors. Structs and unions are meant as simple aggregations of data, or as a way to paint a data structure over hardware or an external type. External types can be defined by the operating system API, or by a file format. Object oriented features are provided with the class data type.

A struct is defined to not have an identity; that is, the implementation is free to make bit copies of the struct as convenient.

Struct, Class Comparison Table Feature struct class C struct C++ struct C++ class

Struct, Class Comparison Table

Feature	struct	class	C struct	C++ struct	C++ class
value type	X		X	X	X
reference type		X
data members	X	X	X	X	X
hidden members		X		X	X
static members	X	X		X	X
default member initializers	X	X
bit fields			X	X	X
non-virtual member functions	X	X		X	X
virtual member functions		X		X	X
constructors		X		X	X
destructors		X		X	X
RAII		X		X	X
operator overloading	X	X		X	X
inheritance		X		X	X
invariants	X	X
unit tests	X	X
synchronizable		X
parameterizable	X	X		X	X
alignment control	X	X
member protection	X	X		X	X
default public	X	X	X	X
tag name space			X	X	X
anonymous	X		X	X	X

结构的声明：

QUOTE:

AggregateDeclaration:
    Tag { DeclDefs }
    Tag Identifier StructBody
    Tag Identifier ;

Tag:
    struct
    union

StructBody:
    { }
    { StructBodyDeclarations }

StructBodyDeclarations:
    StructBodyDeclaration
    StructBodyDeclaration StructBodyDeclarations

StructBodyDeclaration:
    Declaration
    StaticConstructor
    StaticDestructor
    Invariant
    UnitTest
    StructAllocator
    StructDeallocator

StructAllocator:
    ClassAllocator

StructDeallocator:
    ClassDeallocator

它们同在 C 中的结构基本一样，除了以下一些例外：
没有位域
可以显式指定对齐
没有单独的标记名字空间 —— 标记名并入当前的作用域
如下面这样的声明：

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CODE:

struct ABC x;

不允许这样使用：( 本文出处: http://www.d-programming-language-china.org )

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CODE:

ABC x;

匿名结构/联合可以作为其他结构/联合的成员存在
可以为成员提供默认初始值
可以拥有成员函数和静态成员

Static Initialization of Structs结构的静态初始化

如果不提供初始值，静态结构成员会被默认地初始化为成员类型的初始值。如果提供了静态初始值，成员会按照这样的语法初始化：成员名，冒号，表达式。成员可以按照任意顺序初始化。没有出现在初始化列表中的成员会被默认值初始化。( 本文出处: http://www.d-programming-language-china.org )

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CODE:

struct X { int a; int b; int c; int d = 7;}
static X x = { a:1, b:2};            // c 被设置为 0, d 为 7
static X z = { c:4, b:5, a:2 , d:5};            // z.a = 2, z.b = 5, z.c = 4, z.d = 5

C 风格的初始化，依赖于结构声明中的成员的顺序，也是被支持的：

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CODE:

static X q = { 1, 2 };        // q.a = 1, q.b = 2, q.c = 0, q.d = 7

Static Initialization of Unions联合的静态初始化

联合需要显式地初始化。

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CODE:

union U { int a; double b; }
static U u = { b : 5.0 };        // u.b = 5.0

如果联合的其他成员占用的存储空间更大，剩下的部分被初始化为零。( 本文出处: http://www.d-programming-language-china.org )

Dynamic Initialization of Structs结构的动态初始化

结构可以被同类型值动态初始化：

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CODE:

struct S { int a; }
S t;    // default initialized
t.a = 3;
S s = t;    // s.a is set to 3

If opCall is overridden for the struct, and the struct is initialized with a value that is of a different type, then the opCall operator is called:

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CODE:

struct S
{    int a;

    static S opCall(int v)
    {    S s;
    s.a = v;
    return s;
    }

    static S opCall(S v)
    {    S s;
    s.a = v.a + 1;
    return s;
    }
}

S s = 3;    // sets s.a to 3
S t = s;    // sets t.a to 3, S.opCall(s) is not called

Struct Properties结构属性

.sizeof 以字节为单位的结构大小
.alignof 要对齐到的边界值
.tupleof Gets type tuple of fields

Struct Field Properties结构域属性

.offsetof 从结构开始的字节偏移量

of struct( lastupdate:20070426　最新文章请访问http://www.d-programming-language-china.org )

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