Cplusplus 简明教程

C++ Structures (struct)

C/C++ 数组允许为相同类型的多个数据项定义变量，但 structure 是另一种用户定义的数据类型，允许为不同类型的多个数据项定义变量。

C/C++ arrays allow you to define variables that combine several data items of the same kind, but structure is another user defined data type which allows you to combine data items of different kinds.

结构用于表示记录，假设你想为图书馆中的书籍进行管理。你可能想为每本书追踪以下属性 −

Structures are used to represent a record, suppose you want to keep track of your books in a library. You might want to track the following attributes about each book −

Title
Author
Subject
Book ID

Defining a Structure

为定义结构，必须使用 struct 语句。struct 语句定义了包含多个成员的新数据类型。struct 语句的格式如下 −

To define a structure, you must use the struct statement. The struct statement defines a new data type, with more than one member, for your program. The format of the struct statement is this −

struct [structure tag] {
   member definition;
   member definition;
   ...
   member definition;
} [one or more structure variables];

structure tag 是可选的，每个成员定义都是常规变量定义，如 int i; 或 float f; 或任何其他有效的变量定义。在结构定义的最后，在最终的分号前，你可以指定一个或多个结构变量，但这是可选的。以下是你声明 Book 结构的方式 −

The structure tag is optional and each member definition is a normal variable definition, such as int i; or float f; or any other valid variable definition. At the end of the structure’s definition, before the final semicolon, you can specify one or more structure variables but it is optional. Here is the way you would declare the Book structure −

struct Books {
   char  title[50];
   char  author[50];
   char  subject[100];
   int   book_id;
} book;

Accessing Structure Members

为访问结构的任何成员，我们使用 member access operator (.) 。成员访问运算符在结构变量名称与我们想要访问的结构成员之间表示为一个句点。可以使用 struct 关键字为结构类型定义变量。以下是解释结构使用方式的示例 −

To access any member of a structure, we use the member access operator (.). The member access operator is coded as a period between the structure variable name and the structure member that we wish to access. You would use struct keyword to define variables of structure type. Following is the example to explain usage of structure −

#include <iostream>
#include <cstring>

using namespace std;

struct Books {
   char  title[50];
   char  author[50];
   char  subject[100];
   int   book_id;
};

int main() {
   struct Books Book1;        // Declare Book1 of type Book
   struct Books Book2;        // Declare Book2 of type Book

   // book 1 specification
   strcpy( Book1.title, "Learn C++ Programming");
   strcpy( Book1.author, "Chand Miyan");
   strcpy( Book1.subject, "C++ Programming");
   Book1.book_id = 6495407;

   // book 2 specification
   strcpy( Book2.title, "Telecom Billing");
   strcpy( Book2.author, "Yakit Singha");
   strcpy( Book2.subject, "Telecom");
   Book2.book_id = 6495700;

   // Print Book1 info
   cout << "Book 1 title : " << Book1.title <<endl;
   cout << "Book 1 author : " << Book1.author <<endl;
   cout << "Book 1 subject : " << Book1.subject <<endl;
   cout << "Book 1 id : " << Book1.book_id <<endl;

   // Print Book2 info
   cout << "Book 2 title : " << Book2.title <<endl;
   cout << "Book 2 author : " << Book2.author <<endl;
   cout << "Book 2 subject : " << Book2.subject <<endl;
   cout << "Book 2 id : " << Book2.book_id <<endl;

   return 0;
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

Book 1 title : Learn C++ Programming
Book 1 author : Chand Miyan
Book 1 subject : C++ Programming
Book 1 id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Yakit Singha
Book 2 subject : Telecom
Book 2 id : 6495700

Structures as Function Arguments

你可以以非常相似于传递其他变量或指针的方式将结构作为函数实参传递。你可以以访问上述示例中变量的类似方式访问结构变量 −

You can pass a structure as a function argument in very similar way as you pass any other variable or pointer. You would access structure variables in the similar way as you have accessed in the above example −

#include <iostream>
#include <cstring>

using namespace std;
void printBook( struct Books book );

struct Books {
   char  title[50];
   char  author[50];
   char  subject[100];
   int   book_id;
};

int main() {
   struct Books Book1;        // Declare Book1 of type Book
   struct Books Book2;        // Declare Book2 of type Book

   // book 1 specification
   strcpy( Book1.title, "Learn C++ Programming");
   strcpy( Book1.author, "Chand Miyan");
   strcpy( Book1.subject, "C++ Programming");
   Book1.book_id = 6495407;

   // book 2 specification
   strcpy( Book2.title, "Telecom Billing");
   strcpy( Book2.author, "Yakit Singha");
   strcpy( Book2.subject, "Telecom");
   Book2.book_id = 6495700;

   // Print Book1 info
   printBook( Book1 );

   // Print Book2 info
   printBook( Book2 );

   return 0;
}
void printBook( struct Books book ) {
   cout << "Book title : " << book.title <<endl;
   cout << "Book author : " << book.author <<endl;
   cout << "Book subject : " << book.subject <<endl;
   cout << "Book id : " << book.book_id <<endl;
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

Book title : Learn C++ Programming
Book author : Chand Miyan
Book subject : C++ Programming
Book id : 6495407
Book title : Telecom Billing
Book author : Yakit Singha
Book subject : Telecom
Book id : 6495700

Pointers to Structures

你可以以非常相似于为任何其他变量定义指针的方式为结构定义指针，如下所示 −

You can define pointers to structures in very similar way as you define pointer to any other variable as follows −

struct Books *struct_pointer;

现在，你可以将结构变量的地址存储在上面定义的指针变量中。为查找结构变量的地址，将 & 运算符放在结构名称之前，如下所示 −

Now, you can store the address of a structure variable in the above defined pointer variable. To find the address of a structure variable, place the & operator before the structure’s name as follows −

struct_pointer = &Book1;

为使用指向该结构的指针访问结构的成员，必须使用 → 运算符，如下所示 −

To access the members of a structure using a pointer to that structure, you must use the → operator as follows −

struct_pointer->title;

让我们用结构指针重写上面的示例，希望这能让你更容易理解该概念 −

Let us re-write above example using structure pointer, hope this will be easy for you to understand the concept −

#include <iostream>
#include <cstring>

using namespace std;
void printBook( struct Books *book );

struct Books {
   char  title[50];
   char  author[50];
   char  subject[100];
   int   book_id;
};
int main() {
   struct Books Book1;        // Declare Book1 of type Book
   struct Books Book2;        // Declare Book2 of type Book

   // Book 1 specification
   strcpy( Book1.title, "Learn C++ Programming");
   strcpy( Book1.author, "Chand Miyan");
   strcpy( Book1.subject, "C++ Programming");
   Book1.book_id = 6495407;

   // Book 2 specification
   strcpy( Book2.title, "Telecom Billing");
   strcpy( Book2.author, "Yakit Singha");
   strcpy( Book2.subject, "Telecom");
   Book2.book_id = 6495700;

   // Print Book1 info, passing address of structure
   printBook( &Book1 );

   // Print Book1 info, passing address of structure
   printBook( &Book2 );

   return 0;
}

// This function accept pointer to structure as parameter.
void printBook( struct Books *book ) {
   cout << "Book title : " << book->title <<endl;
   cout << "Book author : " << book->author <<endl;
   cout << "Book subject : " << book->subject <<endl;
   cout << "Book id : " << book->book_id <<endl;
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

Book title : Learn C++ Programming
Book author : Chand Miyan
Book subject : C++ Programming
Book id : 6495407
Book title : Telecom Billing
Book author : Yakit Singha
Book subject : Telecom
Book id : 6495700

The typedef Keyword

有一种更简单的方法来定义结构，或者你可以为创建的类型指定“别名”。例如 −

There is an easier way to define structs or you could "alias" types you create. For example −

typedef struct {
   char  title[50];
   char  author[50];
   char  subject[100];
   int   book_id;
} Books;

现在，你可以直接使用 Books 来定义 Books 类型变量，而无需使用 struct 关键字。以下是示例 −

Now, you can use Books directly to define variables of Books type without using struct keyword. Following is the example −

Books Book1, Book2;

你还可以对非结构使用 typedef 关键字，如下所示 −

You can use typedef keyword for non-structs as well as follows −

typedef long int *pint32;

pint32 x, y, z;

x、y 和 z 都是指向 long int 的指针。

x, y and z are all pointers to long ints.