“This is the seventh day of my participation in the August More Text Challenge. For details, see: August More Text Challenge.”

1 structure

  • It is a construct type, and the members in the structure are contiguously contiguously in memory, but the types of the members in the structure may or may not be the same.
  • Define format:
struct student{
    char name[20];int age;
    char sex;
};
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  • Define variables using structures

struct student p1,p3; // int p1;

struct student *p2 = &p1; // int *p2 = &p1;

  • Assign a value to a member of a structure variable
strcpy(p1.name ,"zhangsan");
p1.age  = 25;
p1.sex  = 'm';

strcpy(p2->name ,"zhangsan");
p2->age  = 25;
p2->sex  = 'm';
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  • Struct: is the keyword of a structure
  • Student: type name
  • {} : The contents inside are the members of the structure
  • ; The end of the structure needs to be added;
  • Member types: The types of members in the structure can be different, and can be arbitrary
  • struct student p1; Struct student p1 (struct student
  • . : Access members of a structure through a structure variable
  • -> : If the pointer variable is a structure, access the inside members through ->

2 Array of structures

struct student p1;      //int p1;
struct student p1[2].   //int p1[2];
	
p1[0].name
p1[0].age
p1[0].sex
	
p1[1].name
p1[1].age
p1[1].sex
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3. Use of structures

3.1 Define variables while defining structures

struct student{
    char name[20];int age;
    char sex; 
}p1,p2[2],*p3;  
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☞ defines the variable p1, the array P2 [2], and the pointer p3.

3.2 Unknown structures

struct {
    char name[20];int age;
    char sex;
}p1,p2[2],*p3;	
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☞ defines the variable p1, the array P2 [2], and the pointer p3. You cannot use struct types to define other variables.

3.3 Structure combined with typedef

typedef struct student{
    char name[20];int age;
    char sex;
}stu_t;  / / type
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☞ stu_t p1. Stu_t *p2; // A pointer to p2 is defined

typedef struct {
    char name[20];int age;
    char sex;
}stu_t; / / type
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☞ stu_t p1. Stu_t *p2; // A pointer to p2 is defined

3.4 Assignment of struct variables

3.4.1 Define first and then assign

struct student{
    char name[20];int age;
    char sex; 
};  
			
struct student p1;
			
strcpy(p1.name,"zhangsan");
p1.age = 20;
p1.sex = 'm';
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3.4.2 Simultaneous assignment of defined values

struct student{
    char name[20];int age;
    char sex; 
};  
			
struct student p1 = {
    "zhangsan".20.'m'
};
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Rule 3.4.3. Is assigned to the form

struct student{
    char name[20];int age;
    char sex; 
};  
			
struct student p1 = {
    .name = "zhangsan",
    .sex = 'm'
};
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▌ You can specify a member to be assigned, and ignore members that do not want to be assigned

3.4.4 Define types Define variables and assign values

struct student{
    char name[20];int age;
    char sex; 
}p1 = {
    "zhangsan".20.'m'
};  
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3.4.5 Define a type and define a variable andAssign across members

struct student{
    char name[20];int age;
    char sex; 
}p1 = {
    .name = "zhangsan",
    .sex = 'm'
}; 
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3.5 Assignment of struct arrays

3.5.1 Define and then assign

struct student p1[2].   //int p1[2];
		
p1[0].name
p1[0].age
p1[0].sex
		
p1[1].name
p1[1].age
p1[1].sex
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3.5.2 Simultaneous assignment of the definition

struct student p1[2] ={{"zhangsan".20.'m'},
    {"lisi".30.'w'}};struct student p1[2] = {
    {
    .name = "zhangsan",
    .age  = 20,
    .sex  = 'm'
    },
    {
    .name = "lisi",
    .sex  = 'w'}};Copy the code

3.5.3 DefinitionsSkip member assignment

struct student p1[3] ={[0] = {
    .name = "zhangsan",
    .age  = 20,
    .sex  = 'm'},2] = {
    .name = "lisi",
    .sex  = 'w'}};Copy the code

4 Nesting of structures

struct aa{
    int a;
    int b;
    int c;
};
typedef struct{
    char name[20];int age;
    char sex; 
    int score;
    struct aa t;
}stu_t;
		
typedef struct{
    stu_t stu[30];
    int n;   // Number of students in the current class
}class_t;
	
class_t cls;
cls.stu[0].name
cls.stu[0].age
cls.stu[0].sex
cls.stu[0].score
cls.stu[0].t.a = 10;
cls.stu[0].t.b = 10;
cls.stu[0].t.c = 10; . cls.stu[29]
	
cls.n
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Combination of structure and function pointer

The ☞ struct cannot write functions inside, but it can write function Pointers. Cause: The memory size of the function is uncertain.

struct operations{
    int (*open)(void);
    int (*read)(void);
    int (*write)(void);
    int (*close)(void);
};
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Struct pointer array, struct array pointer

6.1 Array of structure Pointers

typedef struct{
    char name[20];int age;
    char sex; 
    int score;
    struct aa t;
}stu_t;
	
stu_t *p[3];  // Array of struct Pointers
p[0] = malloc(sizeof(stu_t));
p[1] = malloc(sizeof(stu_t));
p[2] = malloc(sizeof(stu_t));
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6.2 Struct array Pointers

stu_t (*p)[3]; // It is a pointer to a row.
stu_t arr[4] [3];
p = arr;
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7 Memory size used by structures

📌 1. If the members inside the structure are less than or equal to 4 bytes, align with the largest member.

2. If there are more than 4 bytes of members in the structure, all members are aligned in four-byte order

3. If there is a char short occupying 4 bytes inside the structure, the second member is always stored from the even position

8 Commons (consortium)

  • Commons: This is a construct type in which all members within the Commons share the number of bytes occupied by the largest member.

  • Define format:

union aa{
    char a;
    short b;
    int c;
    double d;
};
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  • Define variables:

union aa a;

union aa *b;

  • Initialization:

a.a = 'c'; 或者 a.d = 3.1415926;

b = malloc(sizeof(*b));

B - > d = 3.1415925;

  • The role of the union? (Space saving)
struct class{
    struct person p[30].
    int n;
};
	
struct person{
    char name[20];
    int age;
    char sex;
union a{
    int score;
    int salar;
    }b;			
}
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