C++ 数据结构

C++ 数据结构

C/C++ 数组允许您定义将多个相同类型的数据项组合在一起的变量,但是结构是一种另外的用户自定义数据类型,它允许您组合不同类型的数据项。

结构用于表示记录,假设您想要在图书馆中跟踪您的书籍。您可能想要跟踪每本书的以下属性 –

  • 标题
  • 作者
  • 主题
  • 书籍ID

定义结构

要定义结构,您必须使用 struct 语句。struct 语句为您的程序定义了一个具有多个成员的新数据类型。struct 语句的格式如下 –

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

结构标签是可选的,每个成员定义都是一个常规的变量定义,比如int i;或float f;或任何其他有效的变量定义。在结构定义的末尾,在最后一个分号之前,您可以指定一个或多个结构变量,但这是可选的。下面是声明Book结构的方式 –

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

访问结构成员

要访问结构的任何成员,我们使用成员访问运算符(.)。成员访问运算符被编码为在结构变量名和我们希望访问的结构成员之间的句点。您可以使用struct关键字来定义结构类型的变量。以下是用来解释结构用法的示例:

#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;
}

当上述代码被编译并执行时,它会产生以下结果−

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

结构体作为函数参数

您可以像传递任何其他变量或指针一样传递结构体作为函数参数。您可以像在上面的示例中访问结构体变量一样访问它们。

#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;
}

当以上代码被编译和执行时,它产生以下结果 –

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

结构体指针

您可以以非常类似的方式定义指向结构体的指针,就像您定义指向其他任何变量的指针一样,如下所示 –

struct Books *struct_pointer;

现在,您可以将一个结构变量的地址存储在上面定义的指针变量中。要找到一个结构变量的地址,可以在结构的名称前加上 & 运算符,如下所示−

struct_pointer = &Book1;

使用指向结构体的指针来访问结构体的成员,您必须使用- > 操作符,如下所示−

struct_pointer->title;

让我们使用结构指针重新编写上面的示例,希望这样对你理解概念更容易-

#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;
}

在编译和执行以上代码时,会产生以下结果:-

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

typedef 关键字

定义结构体或者“别名”创建的类型有一个更简单的方法。例如:

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

现在,您可以直接使用 Books 定义 Books 类型的变量,而无需使用struct关键字。以下是一个示例−

Books Book1, Book2;

您可以使用 typedef 关键字来定义非结构体,如下所示 –

typedef long int *pint32;

pint32 x, y, z;

x、y和z都是指向长整型的指针。

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