C language: 15. Structure

1、 Structure definition

The way structure is defined ：

	// The way 1
    struct weapon{
    
        char *name;
        int price;
    };
    struct weapon weapon_1 = {
    18};
    weapon_1.name = "asdf";
    // The way 2
    struct weapon2{
    
        char name[20];
        int price;
    }weapon2_1;
    printf("%d \n", weapon2_1.price);
    struct weapon2 wp = {
    "abcccc",123};

    // The way 3
    struct{
    
        char name[20];
        int price;
    }struct_var;
    printf("%d \n",struct_var.price);

coordination typedef Defining structure ：

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2、 Structure initialization and use

struct weapon{
    
	char name[20];
	int atk;
	int price;
}

struct weapon weapon_1 = {
    " weapons 1",100,200};
weapon_1.price++;
printf("%s The price of is ：%d\n",weapon_1.name, weapon_1.price);

3、 Array of structs

struct weapon{
    
	char name[20];
	int price;
}
struct weapon weapon_1[2] = {
    
	" weapons 1",100,
	" weapons 2",200
};
struct weapon weapon_2[2] = {
    
	{
    " weapons 1",100},
	{
    " weapons 2",200}
}; 
printf("%s The price of is ：%d\n", weapon_1[0].name, weapon_1[1].price);

4、 Structure pointer

The pointer points to the structure variable

struct weapon{
    
	char name[20];
	int price;
};
struct * w;
struct weapon weapon1 = {
    " weapons 1", 100};
w = &weapon1;
printf(" weapons %s The price of is %d\n", (*w).name, (*w).price );
// The upper and lower methods of accessing structure pointer are equivalent 
printf(" weapons %s The price of is %d\n",  w->name, w->price );

The pointer points to the structure array

#include <stdio.h>
struct weapon {
    
    char name[20];
    int price;
};
int main(){
    
    struct weapon wea_arr1[2] = {
    
        " net ",200,
        " Dragon Slayer ",201
    };
    struct weapon *p;
    p = wea_arr1;
    printf("[%s] The price of is [%d]\n", (*p).name, (*p).price );
    p++;
    printf("[%s] The price of is [%d]\n", p->name, p->price );
    return 0;
}

5、 Structure memory alignment

	typedef struct {
    
        char a;//1
        char b;//1
        int c;//4
        short d;//2
        double e;//8
    } Align;
    Align align = {
    'a','b',3,4,5.0};
    typedef struct {
    
        char a;//1
        char b;//1
        short d;//2
        int c;//4
        double e;//8
    } Align2;
    Align2 align2 = {
    'a','b',3,4,5.0};

The above example shows , Defining the same types together in the structure can save memory .
Except that the same types are defined together , Different editors , Different c Language versions define different ways of memory alignment optimization , Such as ：

#pragma pack(2) // Almost all editors support this writing , Take effect globally after use 
struct Person{
    
	char *name
	__attribute((aligned(2))) int c;// Only gcc Be able to use （ Align only one field ）
	_Alignas(4) int c;// Only c11 have access to （ Align only one field ）
}