Please answer c language - structure [getting started]

Keywords: C Back-end


1. Declaration of structure

1.1 basic knowledge of structure

The objects we see in life are complex objects, such as describing a cat or a book. We can't use simple type or floating point type to describe these types

1.2 declaration of structure

struct tag
{
member-list;
}variable-list;

Let's say I want to describe a pokemon

I need to describe it from a variety of characteristics, such as name, Atlas number, height or weight

First creation method

struct Pokemon
{
	char name[20];//name
	int id;//Atlas No
	float height; //height
	float weight;//weight
	char fighting_type[20]; //attribute
	char species[15]; //type
};
int main()
{
	struct Pokemon pikachu;//Take this structure to create a variable. The variable type is this structure Pokemon
    return 0;
}

The second creation method

struct Pokemon
{
	char name[20];//name
	int id;//Atlas No
	float height; //height
	float weight;//weight
	char fighting_type[20]; //attribute
	char species[15]; //type
}pokemon1´╝îpokemon2;//overall situation

The difference between the two creation methods is that the structure variables created by the second creation method are global

1.3 types of structure members

The members of a structure can be scalars, arrays, pointers, or even other structures

1.4 definition and initialization of structure variables

Like arrays, structures are initialized, defined in the order and type previously defined

struct Pokemon pikachu = { "Pikachu",25,0.4,6.0,"electric","mouse pokemon" };

2. Access of structure members

I've written it before, so I won't write it in detail

  • Structure variable access member

Members of structure variables are accessed through the point operator (.). The point operator accepts two operands.

struct S s;
strcpy(s.name, "zhangsan");//Use. To access the name member
s.age = 20;//Use. To access age members

Or output

printf("name = %s id = %d height = %.1f weight = %.1f\n", pikachu.name, pikachu.id, pikachu.height, pikachu.weight);

  • Structure pointers access members that point to variables

Sometimes what we get is not a structure variable, but a pointer to a structure (- >).

struct Pokemon* ps = &pikachu;//Structure pointer
	printf("name = %s id = %d height = %.1f weight = %.1f\n", ps->name, ps->id, ps->height, ps->weight);
	printf("name = %s id = %d height = %.1f weight = %.1f\n", (*ps).name, (*ps).id, (*ps).height, (*ps).weight);

3. Structure transmission parameters

When we need to pass parameters to Print the array, which Print function will be better

struct S
{
	int arr[1000];
	float f;
	char ch[100];
};

void print1(struct S tmp)
{
	int i = 0;
	for (i = 0; i < 10; i++)
	{
		printf("%d ", tmp.arr[i]);
	}
	printf("\n");
	printf("%f\n", tmp.f);
	printf("%s\n", tmp.ch);
}

void print2(struct S* ps)
{
	int i = 0;
	for (i = 0; i < 10; i++)
	{
		printf("%d ", ps->arr[i]);
	}
	printf("\n");
	printf("%f\n", ps->f);
	printf("%s\n", ps->ch);
}
int main()
{
	struct S s = { {1,2,3,4,5,6,7,8,9,10}, 5.5f, "Hello there" };
	print1(s);
	print2(&s); 
	return 0;
}

print1 is a value transfer parameter, so a temporary copy will be created, but re creating a space will cause a waste of space. If the content contained in the structure is large enough, it will lead to problems

print2 is address passing, so you don't need to create an entire structure, just a pointer. When the structure is large enough, the efficiency of saving space will be very high.

The following is a professional explanation:

  • When a function passes parameters, the parameters need to be pressed on the stack.
    If the structure is too large when passing a structure object, the system overhead of parameter stack pressing is relatively large, which will lead to performance degradation.

When the program is running, the process of function stack is

For example, execute such a piece of code

int Add(int x, int y)
{
	int z = 0;
	z = x + y;
	return z;
}

int main()
{
	int a = 10;
	int b = 20;
	int c = Add(a, b);
	printf("%d\n", c);
	return 0;
}

The process of program execution is to create from bottom to top and from first to last in the stack according to the code order of the main function

Summary:

Generally, it is a better choice if we use the address when passing the parameter structure

summary

The old fellow must have a good commentary.

Posted by delayedinsanity on Thu, 18 Nov 2021 19:41:02 -0800