C语言-结构体

结构体是什么 ?

结构体是一种构造数据类型，把不同的数据类型整合起来成为一个自定义的数据类型类似于Java中的类

写法1

struct Man{
    char* name;
    int age;
    char nationality[50];
    int(*func)();
};

void main(){
    //初始化结构体变量

    //形式1 只能在变量声明时赋值
    //struct Man m1 = { "Jack", 21 };

    //形式2
    struct Man m1;
    m1.age = 25;
    m1.name = "Heiko";
    strcpy(m1.nationality, "China"); //char nationality[50];需要以这种方式赋值
    printf("%s,%d\n", m1.name, m1.age);

    struct Man m2 = m1;

    getchar();
}

写法2

m3代表一个结构体变量的名称，全局变量，在整个文件都可以使用

struct Man2{
    char* name;
    int age;
}m3;   

void main(){
    m3.name = "Hello";
    printf("%s,%d\n", m3.name, m3.age);
    getchar();
}

写法3

全局变量，在整个文件都可以使用

struct Man3{
    char* name;
    int age;
}m4, m5 = {"jack",20};

写法4 匿名结构体

作用: 控制结构体变量的个数 (限量版) ，相当于单例

struct {
    char* name;
    int age;
} m6;

结构体的嵌套

struct Teacher{
    char* name;
    int age;
};

struct Student{
    char* name;
    int age;
    struct Teacher t;
};

void main(){
    struct Student s1 = { "jack", 21, { "Jason" ,50} };


    struct Teacher t2;
    t2.name = "Jason2";
    t2.age = 51;
    struct Student s2;
    s2.age = 22;
    s2.name = "jack2";
    s2.t = t2;

    printf("学生s2 %s,%d\n",s2.name,s2.age);
    printf("老师t2 %s,%d\n", s2.t.name, s2.t.age);
    getchar();
}

结构体和指针

struct Man4{
    char* name;
    int age;
};

void main(){
    struct Man4 m1 = { "Jack", 30 };
    //结构体指针
    struct Man4 *p = &m1;
    printf("%s,%d\n", m1.name, m1.age);
    printf("%s,%d\n", (*p).name, (*p).age);
    //-> (箭头)是"(*p)."的简写
    printf("%s,%d\n", p->name, p->age);
}

指针与结构体数组

struct Man5{
    char* name;
    int age;
};  

void main(){
    struct Man5 mans[] = { { "A", 20 }, "B", 19 };
    //遍历数组

    //方式1
    struct Man5 *p = mans;
    for (; p<mans+2; p++)   {
        printf("%s,%d\n", p->name, p->age);
    }

    //方式2
    int i = 0;
    for (; i<sizeof(mans)/sizeof(struct Man5); i++) {
        printf("%s,%d\n", mans[i].name, mans[i].age);
    }
}

结构体大小

结构体变量的大小,必须是最宽基本数据类型的整数倍 (提升读取效率)
比如以下 int 4字节，double8字节，共12字节，不够，会填充字节，占用16字节

struct Man6{
    int age;
    double weight;
};

void main(){
    struct Man6 m1 = {20,89.0};
    printf("%#x,%d\n", &m1, sizeof(m1)); //输出结果: 0x6ffd8c,16
    getchar();
}

结构体和内存分配

void main(){
    struct Man *m_p = (struct Man*)malloc(sizeof(struct Man) * 10);
    struct Man *p = m_p;
    //赋值
    p->name = "Jack";
    p->age = 20;
    p++;
    p->name = "Rose";
    p->age = 20;
    struct Man *loop_p = m_p;
    for (; loop_p < m_p+2; loop_p++)
    {
        printf("%s,%d\n", loop_p->name, loop_p->age);
    }
    free(m_p);
    getchar();
}

结构体函数指针成员

可以把结构作为函数参数，传参方式与其他类型的变量或指针类似，这样可以动态执行需要的函数。

struct Girl{
    char* name;
    int age;
    //函数指针
    void(*sayHi)(char*);
};

typedef struct Girl* GirlP;

void sayHi(char* text){
    MessageBoxA(0,text,"title",0);
}

void renameGirlName(GirlP gp1){
    gp1->name = "Lily";
}

void main(){
    struct  Girl g1;
    g1.name = "Lucy";
    g1.age = 18;
    g1.sayHi = sayHi;

    g1.sayHi("hello");

    GirlP gp = &g1;
    renameGirlName(gp);
    gp->sayHi("Good");
    getchar();
}