C语言中结构与结合的区别

C语言中的结构是一种用户定义的数据类型，它允许组合不同类型的数据项。结构用于表示一个记录。

定义结构:要定义结构，必须使用struct语句。struct语句定义了一个新的数据类型，具有一个以上或等于一个成员。struct语句的格式如下:

   struct [structure name]
   {
       member definition;
       member definition;
       ...
       member definition;
   };

   (OR)

   struct [structure name]
   {
       member definition;
       member definition;
       ...
       member definition;
   }structure variable declaration;

C语言中的Union是C语言中可用的一种特殊数据类型，它允许在同一内存位置存储不同的数据类型。可以定义具有多个成员的联合，但在任何给定时间，只有一个成员可以包含值。联合提供了一种将同一内存位置用于多种目的的有效方法。

定义联合体

要定义联合，必须以与定义结构相同的方式使用联合语句。联合语句为程序定义了一个具有多个成员的新数据类型。union statement的格式如下:

    union [union name]
    {
       member definition;
       member definition;
       ...
       member definition;
    };

    (OR) 

    union [union name]
    {
       member definition;
       member definition;
       ...
       member definition;
    }union variable declaration;

结构与联合的相似性

两者都是用户定义的数据类型，用于将不同类型的数据存储为单个单元。
它们的成员可以是任何类型的对象，包括其他结构以及联合或数组。成员也可以由位域组成。
结构体和联合体都只支持赋值=和sizeof操作符。赋值中的两个结构或联合必须具有相同的成员和成员类型。
结构或联合可以按值传递给函数，也可以按值由函数返回。实参必须具有与函数形参相同的类型。结构或联合是通过值传递的，就像标量变量作为相应的参数一样。
”。的操作符或选择操作符，具有最高优先级之一，用于访问用户定义数据类型中的成员变量。

Structure和Union的区别如下表所示，如下表所示:

C语言中结构与结合的区别

// C program to illustrate differences
// between structure and Union
 
#include <stdio.h>
#include <string.h>
  
// declaring structure
struct struct_example
{
    int integer;
    float decimal;
    char name[20];
};
  
// declaring union
  
union union_example
{
    int integer;
    float decimal;
    char name[20];
};
  
void main()
{
    // creating variable for structure
    // and initializing values difference
    // six
    struct struct_example s={18,38,"geeksforgeeks"};
  
    // creating variable for union
    // and initializing values
    union union_example u={18,38,"geeksforgeeks"};
  
          
    printf("structure data:\n integer: %d\n"
                "decimal: %.2f\n name: %s\n",
                s.integer, s.decimal, s.name);
    printf("\nunion data:\n integer: %d\n"
                 "decimal: %.2f\n name: %s\n",
                u.integer, u.decimal, u.name);
  
  
    // difference two and three
    printf("\nsizeof structure : %d\n", sizeof(s));
    printf("sizeof union : %d\n", sizeof(u));
      
    // difference five
    printf("\n Accessing all members at a time:");
    s.integer = 183;
    s.decimal = 90;
    strcpy(s.name, "geeksforgeeks");
      
    printf("structure data:\n integer: %d\n "
                "decimal: %.2f\n name: %s\n",
            s.integer, s.decimal, s.name);
      
    u.integer = 183;
    u.decimal = 90;
    strcpy(u.name, "geeksforgeeks");
      
    printf("\nunion data:\n integer: %d\n "
                "decimal: %.2f\n name: %s\n",
            u.integer, u.decimal, u.name);
      
    printf("\n Accessing one member at time:");
      
    printf("\nstructure data:");
    s.integer = 240;
    printf("\ninteger: %d", s.integer);
      
    s.decimal = 120;
    printf("\ndecimal: %f", s.decimal);
      
    strcpy(s.name, "C programming");
    printf("\nname: %s\n", s.name);
      
    printf("\n union data:");
    u.integer = 240;
    printf("\ninteger: %d", u.integer);
      
    u.decimal = 120;
    printf("\ndecimal: %f", u.decimal);
      
    strcpy(u.name, "C programming");
    printf("\nname: %s\n", u.name);
      
    //difference four
    printf("\nAltering a member value:\n");
    s.integer = 1218;
    printf("structure data:\n integer: %d\n "
                " decimal: %.2f\n name: %s\n",
                s.integer, s.decimal, s.name);
      
    u.integer = 1218;
    printf("union data:\n integer: %d\n"
           " decimal: %.2f\n name: %s\n",
            u.integer, u.decimal, u.name);
}

输出:

structure data:
 integer: 18
 decimal: 38.00
 name: geeksforgeeks

union data:
 integer: 18
 decimal: 0.00
 name: ?

sizeof structure: 28
sizeof union: 20

 Accessing all members at a time: structure data:
 integer: 183
 decimal: 90.00
 name: geeksforgeeks

union data:
 integer: 1801807207
 decimal: 277322871721159510000000000.00
 name: geeksforgeeks

 Accessing one member at a time:
structure data:
integer: 240
decimal: 120.000000
name: C programming

 union data:
integer: 240
decimal: 120.000000
name: C programming

Altering a member value:
structure data:
 integer: 1218
 decimal: 120.00
 name: C programming
union data:
 integer: 1218
 decimal: 0.00
 name: ?