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Initial structure

2022-06-23 01:43:00 【'Dream_】

If you will It's better to start than to give up . Roman.

May we all have our own goals and are making unremitting efforts for them .

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One 、 Declaration of a structure

One ） Basic knowledge of structure

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 .

Two ） Declaration of a structure

Form like ：

struct tag // struct（ keyword ）+ Structural tag
{
member-list; // Member variables
}variable-list; // Variable list

example ：

// Structure
struct Stu
{
   char name[20]; // name
   int age; // Age
   char sex[8]; // Gender
   float score; // achievement
}s1,s2,s3;
// s1,s2,s3 It's through struct Stu Variable created by type
// s1,s2,s3 Global variable
// typedef Type redefinition / Type renaming
typedef struct Stu Stu;
// You can use Stu Instead of struct Stu
int main()
{
   // struct Stu Is the structure type , You can't omit struct

   struct Stu s4;
   struct Stu s5;
   // s4,s5 It's a local variable

   Stu s6;
   // typedef Can be used after Stu
   return 0;
}

// typedef Another way
struct Stu
{
   char name[20]; // name
   int age; // Age
   char sex[8]; // Gender
   float score; // achievement
}Stu; // At this time, you can only write the name of the heavy life here , Cannot write variable list

3、 ... and ） Type of structure member

Structure members can be Scalar 、 Array 、 The pointer , Even structures .

Four ） Structure variable definition and initialization

1. Structure initialization Curly braces { }

2. Pointer to the variable Address or Vent pointer NULL

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Two 、 Access to structure members

1. Structure member access operator ：

Structural variable . Structure member name
Structure pointer -> Structure member name

2. example ：

//  Structure access 

struct Stu
{
	char name[20];
	int age;
};

void print(struct Stu* ps) {
	printf("name = %s   age = %d\n", (*ps).name, (*ps).age);
	// Use structure pointers to access members that point to objects 
	printf("name = %s   age = %d\n", ps->name, ps->age);
}

int main()
{
	struct Stu s = { "zhangsan", 20 };
	print(&s);// Structure address transfer parameter 
	return 0;
}

//  If the structure has multiple layers   According to   The pointer -> or  Variable .  Just visit

3. modify Member contents of structure variables

Members are ordinary ： =（ assignment ）
Members are arrays ： strcpy（ ,）; // The header file string.h

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3、 ... and 、 Structural parameters

One ） Pass on Structural variable

Pass on Structural variable , namely Value passed ： An argument is a temporary copy of a formal parameter .

It will waste a lot of space
When changing the contents of formal parameters through functions , Arguments don't change , High security

Two ） Pass on Structure pointer

Pass on Structure pointer , namely Address transmission .

Account for only a 4/8 byte , Less space
To improve security , When transferring parameters Add... Before the formal parameter const modification

3、 ... and ） Summary

When a function passes parameters , Parameters need to be stacked .

If you pass a structure object , The structure is too large , The system overhead of parameter stack pressing is large , So it will lead to performance degradation

Each function call will open up a space in the stack area of memory
Memory （ From top to bottom ）：

The stack area ： local variable 、 Function parameter
Heap area ： Dynamic memory development Such as ：malloc 、free 、calloc 、realloc
Static zone ： Static variables 、 Global variables