First understanding of structure

It may be a little cumbersome , But please read it patiently ~~

Before talking about what a structure is , Let's talk about why there is a structure , stay C In language , If we want to create an integer variable , Then we can use int, Want to create a character variable , It can be used char, Want to create a decimal , It can be used float perhaps double, But if we want to describe a person , Or a Book , What to do ？ Take people for example , Describe a person , Need his name 、 Gender 、 Age and so on , These variables are not of the same type , So we can't use simple int perhaps double Wait for keywords to create , So we need a variable type that can meet various types of variables , So the structure comes, but this important task .

So what is a 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 . Its members can be said to be scalars 、 Array 、 The pointer 、 Even another structure .

1. Declaration of a structure

Before using a structure , Need statement , The format is as follows ：

struct stu
{
    
	char name[20];
	char gender[10];
	int age;
};

int main()
{
    
	struct stu s = {
     "hahaha","man",20 };
	return 0;
}

among struct Keyword ,stu Is the name of the structure ,name、gender and age Is a member variable of the structure ,main The structure variable is defined in the function s And give it an initial value .

2. There are also two types

struct stu      //1
{
    
	char name[20];
	char gender[10];
	int age;
}s1;

typedef struct stu     //2
{
    
	char name[20];
	char gender[10];
	int age;
}stu;

stu s2 = {
     "lalala","women",18 };

form 1 After parentheses s1 It's a variable. , Similar to the previous variables s, Can be created directly , But it still needs to be assigned ;
form 2 We should ensure two stu Exactly the same as , Because this is the format requirement , And you can't create variables at the end , But there is no need to add keywords when creating variables in this form struct.

3. Access member variables

When we need to access member variables , Need to use .（ spot ） This symbol , The access format is as follows ：

	printf("%s ", s.name);
	printf("%s ", s.gender);
	printf("%d ", s.age);

4. Structural parameters

We know that the forms of parameter transmission include value transmission and address transmission , Structure is no exception , Go straight to the code ：

void print1(struct stu s)
{
    
	printf("%s\n", s.name);
}

void print2(struct stu* s)
{
    
	printf("%s\n", s->name);
}

int main()
{
    
	struct stu s = {
     "hahaha","man",20 };
	print1(s);
	print2(&s);
	return 0;
}

These two parameter transfer methods can print the results well , Careful people will find that the way of accessing member variables by passing values and addresses is different , For Value Passing Access .（ spot ） This symbol , For address access ->, besides , Byref （&s） Compare and transfer values （s） More space saving , Value passing is the size of the whole structure passed , And value passing is to pass the address of the structure , The size of the address is 4 or 8 Bytes , If there are many members in the structure , Address transmission will save more space .