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C language structure

2022-06-30 18:15:00 【*Thousands of miles of mountains and rivers*】

One 、 Structure

C Language provides basic data structure , for example char 、short 、int 、float.... Other types ; These pairs are called built-in types . How to design your own type ？

such as ： When we define a person , Different attributes of people are more difficult to define with the same data type , Because of people's height 、 Age 、 Attributes such as weight often require different data types , At this time , We introduce the concept of structure

Use a structure to encapsulate some attributes , Design new types , stay C In language, it is called struct type . A structure is a collection of values , These values are called member variables . Each member of a structure can be a variable of a different type

Structure statement （structure declaration）

struct  Structure name 
{
    Member list （ It can be a basic data type , The pointer , Array or other structure type ）
};
/*struct The keyword represents a structure .*/

struct People
{
  char s_id[8];
  char s_name[8];
  char s_sex[4];
  int s_age;
};

Be careful ;

keyword struct Is the data type specifier , Point out that the following is the structure type ;
identifier Student Is the type name of the structure ;
The last semicolon must be written ;

Two 、 Structure definition and initialization

The declaration of the structure is just a simple description , In fact, before the structure type variable is defined , It doesn't allocate space in memory .

 int main()
{
    struct People people;// local variable -- Put it in the stack area 
    return 0;
}

* struct Structure name Structure variable name

A struct is a data type , In other words, it can be used to define variables . Like a “ Templates ”, The variables defined have the same properties . You can compare a structure to “ Drawing ”, Structural variables are compared to “ Spare parts ”, The characteristics of parts produced according to the same drawing are the same ;

A struct is a data type , Is a template for creating variables , It doesn't take up memory space ;
Structural variables contain real data 、 Need storage space ;

3、 ... and 、 Structure member access

Structure variables use . visit ;
Structural variable . object

#include<stdio.h>
#include<string.h>
struct Date
{
	int year;
	int month;
	int day;
};
struct Student
{
	char s_name[20];
	struct Date birthday;
	float score;
};
int main()
{
	struct Student stu = { "liuwen",2000,10,1,99.9 };
	printf("name=%s\nbirtyday=%d.%d.%d\nscore=%f\n", stu.s_name, stu.birthday.year, stu.birthday.month, stu.birthday.day, stu.score);
	stu.score = 77;
	printf("name=%s\nbirtyday=%d.%d.%d\nscore=%f\n", stu.s_name, stu.birthday.year, stu.birthday.month, stu.birthday.day, stu.score);
	return 0;

Be careful ： There are three cases of overall assignment of structural variables

Define structure variables （ use {} initialization ）
Initialize with a defined structure variable
Variables with the same structure type can be assigned to each other as a whole ;

stay C There is no casting of struct type in language .

Four 、 Structure variables and pointers

Built in types can define pointer variables , Structure types can also define structure type pointers ;

The structure type pointer accesses the acquisition and assignment form of the member ：

（1）（*p）. Member name （. Has a higher priority than *,（*p） The brackets on both sides cannot be less ）

（2） p-> Member name （-> Pointer ）

#include<stdio.h>
#include<string.h>
struct Inventory// goods 
{
	char description[20];// Name of goods 
	int quantity;// Inventory data 
};
int main()
{
	struct Inventory sta = { "iphone",20 };
	struct Inventory* stp = &sta;
	char name[20] = { 0 };
	int num = 0;
	(*stp).quantity = 30;
	stp->quantity = 30;
	strcpy_s(name,sizeof(stp->description),stp->description);
	printf("%s %d\n", stp->description, stp->quantity);
	printf("%s %d\n", (*stp).description, (*stp).quantity);
	return 0;
}

Structure and function

#include<stdio.h>
#include<string.h>
#define _CRT_SECURE_NO_WARNINGS
struct School
{
	char s_name[20];// School 
	int s_age;
};
void Print_a(struct School sx)
{
	printf("%s %d\n", sx.s_name, sx.s_age);
}
void Print_c(struct School* sp)
{
	printf("%s %d\n", sp->s_name, sp->s_age);
}
int main()
{
	struct School sx = { "xi'an",100 };
	Print_a(sx);
	Print_c(&sx);
	return 0;
}

5、 ... and 、struct and class The difference between

　 1、 What is? class?

　　class( class ) Is the basic concept of object-oriented programming , Is a custom data structure type , Usually contains fields 、 attribute 、 Method 、 attribute 、 Constructors 、 Indexer 、 Operators, etc. . Because it's a basic concept , So there is no need to describe in detail here , Readers can inquire relevant concepts to understand . What we emphasize is .NET in , All classes eventually inherit from System.Object class , Therefore, it is a reference type , in other words ,new An instance of a class , Object stores the reference address of the actual data of the instance , The value of the object is stored in the managed heap (managed heap) in .

　 2、 What is? struct?

　　struct( structure ) Is a value type , It is used to organize a group of related information variables into a single variable entity . All structures are inherited from System.ValueType class , So it's a value type , in other words ,struct The instance is allocated on the stack of the thread (stack) On , It stores the value itself , Without a pointer to the value . So it's using struct when , We can think of it as int、char Such basic type classes treat .

1. Default inherited permissions ,class According to private Inheritance processing ,struct According to public Inheritance processing ;
2. Default access rights for members .class The default member of is private jurisdiction ,struct The default is public jurisdiction .
3.struct Value type ,class Is object type