c语言void指针

#include 

#include 

typedef struct
{
    int a;
    int b;
} str;

int main(int argc, char *argv[])

{
    void *p;

    str *st, *st1;

    st = (str *)malloc(sizeof(str));

    st->a = 23;

    st->b = 24;

    p = st;

    printf("%dn%dn", ((str *)p)->a, ((str *)p)->b);

    st1 = (str *)p;

    printf("%dn%dn", st1->a, st1->b);

    free(st);

    return 0;
}

        图 一

c语言的void指针指向的具体指针，必须强制转换

如图一的 

# include 
# include
# include 
typedef struct
{
    int year;
    int month;
    int day;
} AGE;

typedef struct 
{
    char name[20];  //姓名
    int num;  //学号
    void *birthday;  
    float score;  //分数
} STUDENT;

int main(void)
{
    STUDENT student1; 
    STUDENT *p = NULL;  
    p = &student1;  
    strcpy(p->name, "小明");
    printf("birth is %xn", p->birthday);
    AGE *bd;
    bd = ( AGE *) malloc(sizeof(AGE));
    printf("sizeof AGE is %drn", sizeof(AGE));
    printf("sizeof STUDENT is %drn", sizeof(STUDENT));

    bd->day = 29;
    bd->year = 1989;
    bd->month = 3;

    p->birthday = bd;
    p->num = 1207041;
    p->score = 100;
    printf("name : %sn", p->name);  //p->name不能写成p
    printf("birthday : %d-%d-%dn", ((AGE *)p->birthday)->year, ((AGE *)p->birthday)->month, ((AGE *)p->birthday)->day);
    printf("num : %dn", p->num);
    printf("score : %.1fn", p->score);
    return 0;
}

图二

图二的

 也是强制转行