Arrays允许定义可以包含多个相同类型的数据项的变量类型.类似地，结构是C中可用的另一种用户定义数据类型，它允许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图书.您可能希望跟踪每本书的以下属性 :
标题
作者
主题
图书编号
要定义结构，必须使用 struct 语句. struct语句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];结构标记是可选的，每个成员定义都是普通的变量定义，例如int i;或漂浮f;或任何其他有效的变量定义.在结构定义的最后，在最后一个分号之前，您可以指定一个或多个结构变量，但它是可选的.这是你宣布书籍结构的方式;
struct Books {
char title[50];
char author[50];
char subject[100];
int book_id;
} book;要访问结构的任何成员，我们使用成员访问运算符( ).的.成员访问运算符被编码为结构变量名称和我们希望访问的结构成员之间的句点.您可以使用关键字 struct 来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时，会产生以下结果 :
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
您可以将结构作为函数参数传递，方法与传递任何其他变量或指针的方式相同.
#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时，会产生以下结果 :
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
您可以像定义指向任何其他变量的指针一样定义结构指针 :
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.要查找结构变量的地址，请放置'&';结构名称前的运算符如下 :
struct_pointer =& Book1;
要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 :
struct_pointer-> title;
让我们使用结构指针重写上面的例子.
#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时，会产生以下结果 :
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
位字段允许在结构中打包数据.当内存或数据存储非常宝贵时，这尤其有用.典型示例包括 :
将多个对象打包到机器字中.例如可以压缩1位标志.
读取外部文件格式 - 可以读入非标准文件格式，例如9位整数.
C允许我们在结构定义中执行以下操作:将变量后面的位长度放入.例如 :
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;这里，packed_struct包含6个成员:四个1位标志f1..f3,4位型和9位my_int.
C尽可能紧凑地自动打包上述位字段，前提是字段的最大长度小于或等于计算机的整数字长.如果不是这种情况，那么一些编译器可能允许字段重叠，而其他编译器会将下一个字段存储在下一个字中.
