C语言 结构体(Struct)

数组允许定义变量的类型,这些变量可以容纳相同种类的多个数据项。同样,结构是C中可用的另一种用户定义的数据类型,它允许组合不同种类的数据项。

结构Struct用于表示记录,假设您想定义图书馆中的书籍,您可能需要定义跟踪有关每本书的以下属性-

  • 标题 title
  • 作者 author
  • 主题 subject
  • 图书ID book_id

定义结构体

要定义结构,必须使用 struct 语句, struct语句定义了一个新数据类型,该数据类型具有多个成员变量, 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普通的变量定义,如int i;或浮动f;或任何其他有效的变量定义。在结构定义的最后,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。这是您声明Book结构的方式-

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

访问结构体

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结构变量名和我们希望访问的结构成员之间的句点。您将使用关键字 struct定义结构类型的变量。以下示例显示如何在程序中使用结构-

 #include <stdio.h>
 #include <string.h>

 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, "C Programming");
    strcpy( Book1.author, "Nuha Ali"); 
    strcpy( Book1.subject, "C Programming Tutorial");
    Book1.book_id=6495407;

    /* book 2 specification */
    strcpy( Book2.title, "Telecom Billing");
    strcpy( Book2.author, "Zara Ali");
    strcpy( Book2.subject, "Telecom Billing Tutorial");
    Book2.book_id=6495700;

    /* print Book1 info */
    printf( "Book 1 title : %s\n", Book1.title);
    printf( "Book 1 author : %s\n", Book1.author);
    printf( "Book 1 subject : %s\n", Book1.subject);
    printf( "Book 1 book_id : %d\n", Book1.book_id);

    /* print Book2 info */
    printf( "Book 2 title : %s\n", Book2.title);
    printf( "Book 2 author : %s\n", Book2.author);
    printf( "Book 2 subject : %s\n", Book2.subject);
    printf( "Book 2 book_id : %d\n", Book2.book_id);

    return 0;
 }

编译并执行上述代码后,将产生以下输出-

Book 1 title : C Programming
Book 1 author : Nuha Ali
Book 1 subject : C Programming Tutorial
Book 1 book_id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Zara Ali
Book 2 subject : Telecom Billing Tutorial
Book 2 book_id : 6495700

函数参数

您可以像传递任何其他变量或指针一样,将结构作为函数参数传递。

#include <stdio.h>
#include <string.h>

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

/* function declaration */
void printBook( struct Books book );

int main( ) {

   struct Books Book1;        /* Declare Book1 of type Book */
   struct Books Book2;        /* Declare Book2 of type Book */

   /* book 1 specification */
   strcpy( Book1.title, "C Programming");
   strcpy( Book1.author, "Nuha Ali"); 
   strcpy( Book1.subject, "C Programming Tutorial");
   Book1.book_id=6495407;

   /* book 2 specification */
   strcpy( Book2.title, "Telecom Billing");
   strcpy( Book2.author, "Zara Ali");
   strcpy( Book2.subject, "Telecom Billing Tutorial");
   Book2.book_id=6495700;

   /* print Book1 info */
   printBook( Book1 );

   /* Print Book2 info */
   printBook( Book2 );

   return 0;
}

void printBook( struct Books book ) {

   printf( "Book title : %s\n", book.title);
   printf( "Book author : %s\n", book.author);
   printf( "Book subject : %s\n", book.subject);
   printf( "Book book_id : %d\n", book.book_id);

编译并执行上述代码后,将产生以下输出-

 Book title : C Programming
 Book author : Nuha Ali
 Book subject : C Programming Tutorial
 Book book_id : 6495407
 Book title : Telecom Billing
 Book author : Zara Ali
 Book subject : Telecom Billing Tutorial
 Book book_id : 6495700

结构体指针

您可以使用与定义任何其他变量的指针相同的方式定义结构的指针-

struct Books *struct_pointer;

现在,您可以将结构变量的地址存储在上面定义的指针变量中。

struct_pointer=&Book1;

要使用指向结构的指针来访问该结构的成员,必须使用->运算符,如下所示:

 struct_pointer->title;

让我们使用结构指针重写以上示例。

 #include <stdio.h>
 #include <string.h>

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

 /* function declaration */
 void printBook( struct Books *book );
 int main( ) {

    struct Books Book1;        /* Declare Book1 of type Book */
    struct Books Book2;        /* Declare Book2 of type Book */

    /* book 1 specification */
    strcpy( Book1.title, "C Programming");
    strcpy( Book1.author, "Nuha Ali"); 
    strcpy( Book1.subject, "C Programming Tutorial");
    Book1.book_id=6495407;

    /* book 2 specification */
    strcpy( Book2.title, "Telecom Billing");
    strcpy( Book2.author, "Zara Ali");
    strcpy( Book2.subject, "Telecom Billing Tutorial");
    Book2.book_id=6495700;

    /* print Book1 info by passing address of Book1 */
    printBook( &Book1 );

    /* print Book2 info by passing address of Book2 */
    printBook( &Book2 );

    return 0;
 }

 void printBook( struct Books *book ) {

    printf( "Book title : %s\n", book->title);
    printf( "Book author : %s\n", book->author);
    printf( "Book subject : %s\n", book->subject);
    printf( "Book book_id : %d\n", book->book_id);
 }

编译并执行上述代码后,将产生以下输出-

Book title : C Programming
Book author : Nuha Ali
Book subject : C Programming Tutorial
Book book_id : 6495407
Book title : Telecom Billing
Book author : Zara Ali
Book subject : Telecom Billing Tutorial
Book book_id : 6495700

位域

位域允许将数据打包在结构中, 当内存或数据存储非常宝贵时,这特别有用。

C允许我们在结构定义中通过在变量后加上:bit长度来做到这一点。如-

struct packed_struct {
   unsigned int f1:1;
   unsigned int f2:1;
   unsigned int f3:1;
   unsigned int f4:1;
   unsigned int type:4;
   unsigned int my_int:9;
} pack;

在这里,packed_struct包含6个成员:四个1位标志f1..f3,一个4位类型和一个9位my_int。

只要该字段的最大长度小于或等于计算机的整数字长,C就会自动尽可能紧凑地打包上述位字段,如果不是这种情况,则某些编译器可能允许字段的内存重叠,而另一些编译器会将下一个字段存储在下一个字中。