当前位置：网站首页>C language - structural basis

C language - structural basis

2022-07-05 22:18:00 【DSTBP】

Structure foundation

Arrays allow you to define storable identical Variables of type data items ,
structure Is another user-defined available data type , It allows you to store Different Data item of type .

One 、 explain

C In language , The structure type belongs to a construction type （ Other construction types are ： An array type , Joint type ）

lead ：

In practical terms , A set of data often has many different data types . for example , Register student information , You may need to use char Type name ,int Type or char Type student number ,int Type of age ,char Type of gender ,float Type achievement .

Structure （ similar “ Record ”）, Can effectively solve this problem .

Concept
Structure is essentially a data type , But it can include several “ member ”, The type of each member can be the same or different , It can also be a basic data type or a construction type .
advantage
Structures can not only record different types of data , And make the data structure “ High cohesion , Low coupling ” Of , It is more conducive to the reading, understanding and transplantation of the program , And the storage mode of the structure can improve CPU Access speed to memory .

Two 、 Statement

struct tag 

{
     
    member-list
    member-list 
    member-list  
    ...
} variable-list ;      // Don't forget that there is a semicolon after the braces

analysis ：

struct The keyword represents a structure .
tag It's the structure label .
member-list Member list , It's the standard variable definition , such as int i; perhaps float f, Or other valid variable definitions .
variable-list Structural variables , The definition is at the end of the structure , Before the last semicolon , You can specify one or more structure variables .
Structure declarations can be placed outside functions （ This is the global structure , Similar to global variables , All functions declared after it can use ）
You can also put it in a function （ This is the local structure , Similar to local variables , Can only be used inside this function , If it has the same name as the global structure , The global structure will be temporarily masked ）.
This declaration only defines the structure type （ What is in the structure int char float）, There are no variables defined （std1 std2）

example

// For example, declare the structure of a student ：

struct Student

{
      

char name[20];    // full name 

int num;     // Student number 

float score;      // achievement 

};	// Pay attention to the semicolon

3、 ... and 、 Structural variables

The definition of structure does not allocate storage space , Structural variables are allocated corresponding storage according to their data structures

struct  Structure name   Structure variable name ;

example

struct Student

{
             

	char name[20];      // full name 
	int num;            // Student number 
	float score;        // achievement 

};
struct Student stu1;    // Define structure variables 

struct Student
{
            
    char name[20];       
    int num;             
    float score;         
}stu1;

// The definition is followed by the variable name

After defining structure variables , The system will allocate memory units , The occupied length is the sum of bytes occupied by variables in the structure , The specific length can be used in the compiler sizeof Find out the keywords respectively .

Four 、 Different forms of structure

tag、member-list、variable-list this 3 At least part of it must appear 2 individual .

The structure is not labeled
```
struct 
{
      
    int a;
    char b;
    double c;
} s1;
```
This method cannot define new structural variables again （s2,s3…）了 .

The structure does not declare variables

struct example
{
      
    int a;
    char b;
    double c;
};

Labeled structure , Variable declared t1、t2、t3
```
struct SIMPLE t1, t2[20], *t3;
```

use typedef Create a new type

typedef struct
{
      
    int a;
    char b;
    double c; 
} Simple2;

// Now we can use Simple2 Declare new struct variables as types 
Simple2 u1, u2[20], *u3;

5、 ... and 、 Access structure members

Point with the structure member operator （.）

General form of accessing members ：
```
 Structure variable name  .  Member name 
```
Such as stu1 . name Students stu1 The name of .

The member in the structure is another structure The form of interview ：

Structure variable name . Structure variable name （…） . Member name
Such as stu1.birthday.year Visit the year of birth

struct Birthday

{
                      
     int year;
     int month;
     int day;
};
struct Student

{
                      
    char name[20];
    int num;
    float score;
    struct Birthday birthday;   // Birthday 
}stu1;

struct Student

{
                      
    char name[20];
    int num;
    float score;
    struct Birthday{
      

    int year;
    int month;
    int day;

} bir1;

}stu1;

Specific operation
example

#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;        /*  Statement  Book1, The type is  Books */
   struct Books Book2;        /*  Statement  Book2, The type is  Books */
 
   /* Book1  detailed  */
   strcpy( Book1.title, "C Programming");
   strcpy( Book1.author, "Nuha Ali"); 
   strcpy( Book1.subject, "C Programming Tutorial");
   Book1.book_id = 6495407;
 
   /* Book2  detailed  */
   strcpy( Book2.title, "Telecom Billing");
   strcpy( Book2.author, "Zara Ali");
   strcpy( Book2.subject, "Telecom Billing Tutorial");
   Book2.book_id = 6495700;
 
   /*  Output  Book1  Information  */
   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);
 
   /*  Output  Book2  Information  */
   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;
}

6、 ... and 、 Initialization of structure variables

The definition is assigned directly

struct Student
{
      
      char name[20];
      char sex;
      int number;
}stu1 = {
      "zhaozixuan",'M',12345};   // Note that the type and order of initialization values should be consistent with the type and order of members when the structure is declared *

struct Student
{
      
	char name[20];
	char sex;
	int number;
};
struct Student stu1 = {
      "zhaozixuan",'M',12345};

After defining the structure, assign values one by one

strcpy(stu1.name, " Wang Wei ");
stu1.sex = 'M';
stu1.number = 12305;

Assign values in any order after definition

struct Student stu1 = 
{
      
  .name = "Wang",
  .number = 12345,
  .sex = 'W', 
 };

Partial initialization

struct Student stu4 = {
      .name = "Lisa"};

Initialize a new structure variable of the same type with an existing structure , Overall copy （ Each member is assigned to the new structure variable one by one ）
```
stu3 = stu1;
```

Be careful
When initializing structure variables , To assign values to structure members one by one , Cannot skip previous member variables , And directly assign initial values to the following members , But you can only assign the first few , For the following unassigned variables , If it's numerical , It will be automatically assigned to 0, For character type , The initial value will be automatically assigned to NULL, namely ‘\0’.

7、 ... and 、 References to structure variables （ Output and input ）

. It's the operator , Highest priority of all operators

printf("%d",stu1.name);

scanf("%d",&stu2.birthday.month);

If the member of the structure itself is a structure , You need to continue to use . Operator , Up to the lowest level .（stu2.birthday.month） correct （stu1.birthday） error

原网站

版权声明
本文为[DSTBP]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/02/202202140436088791.html