int main()
{Person._age = 100;   // 编译失败：error C2059: 语法错误:“.”return 0;
}

6.3 结构体内存对齐规则

        1. 第一个成员在与结构体偏移量为 0 的地址处。

        2. 其他成员变量要对齐到某个数字（对齐数）的整数倍的地址处。

注意：对齐数 = 编译器默认的一个对齐数 与 该成员大小的较小值。

VS 中默认的对齐数为 8

        3. 结构体总大小为：最大对齐数（所有变量类型最大者与默认对齐参数取最小）的整数倍。

        4. 如果嵌套了结构体的情况，嵌套的结构体对齐到自己的最大对齐数的整数倍处，结构体的整体大小就是所有最大对齐数（含嵌套结构体的对齐数）的整数倍。

class Date
{ 
public:void Init(int year, int month, int day){_year = year;_month = month;_day = day;}void Print(){cout <<_year<< "-" <<_month << "-"<< _day <<endl;}
private:int _year;     // 年int _month;    // 月int _day;      // 日
};
int main()
{Date d1, d2;d1.Init(2022,1,11);d2.Init(2022, 1, 12);d1.Print();d2.Print();return 0;
}

// 1.下面程序编译运行结果是？ A、编译报错 B、运行崩溃 C、正常运行
class A
{
public:void Print(){cout << "Print()" << endl;}
private:int _a;
};
int main()
{A* p = nullptr;p->Print();return 0;
}
// 1.下面程序编译运行结果是？ A、编译报错 B、运行崩溃 C、正常运行
class A
{ 
public:void PrintA() {cout<<_a<<endl;}
private:int _a;
};
int main()
{A* p = nullptr;p->PrintA();return 0;
}

typedef int DataType;
typedef struct Stack
{DataType* array;int capacity;int size;
}Stack;
void StackInit(Stack* ps)
{assert(ps);ps->array = (DataType*)malloc(sizeof(DataType) * 3);if (NULL == ps->array){assert(0);return;}ps->capacity = 3;ps->size = 0;
}
void StackDestroy(Stack* ps)
{assert(ps);if (ps->array){free(ps->array);ps->array = NULL;ps->capacity = 0;ps->size = 0;}
}
void CheckCapacity(Stack* ps)
{if (ps->size == ps->capacity){int newcapacity = ps->capacity * 2;DataType* temp = (DataType*)realloc(ps->array, newcapacity*sizeof(DataType));if (temp == NULL){perror("realloc申请空间失败!!!");return;}ps->array = temp;ps->capacity = newcapacity;}
}
void StackPush(Stack* ps, DataType data)
{assert(ps);CheckCapacity(ps);ps->array[ps->size] = data;ps->size++;
}
int StackEmpty(Stack* ps)
{assert(ps);return 0 == ps->size;
}
void StackPop(Stack* ps)
{if (StackEmpty(ps))return;ps->size--;
}
DataType StackTop(Stack* ps)
{assert(!StackEmpty(ps));return ps->array[ps->size - 1];
}
int StackSize(Stack* ps)
{assert(ps);return ps->size;
}
int main()
{Stack s;StackInit(&s);StackPush(&s, 1);StackPush(&s, 2);StackPush(&s, 3);StackPush(&s, 4);printf("%d\n", StackTop(&s));printf("%d\n", StackSize(&s));StackPop(&s);StackPop(&s);printf("%d\n", StackTop(&s));printf("%d\n", StackSize(&s));StackDestroy(&s);return 0;
}

typedef int DataType;
class Stack
{
public:void Init(){_array = (DataType*)malloc(sizeof(DataType) * 3);if (NULL == _array){perror("malloc申请空间失败!!!");return;}_capacity = 3;_    size = 0;}void Push(DataType data){CheckCapacity();_array[_size] = data;_size++;}void Pop(){if (Empty())return;_size--;}DataType Top(){ return _array[_size - 1];}int Empty() { return 0 == _size;}int Size(){ return _size;}void Destroy(){if (_array){free(_array);_array = NULL;_capacity = 0;_size = 0;}}
private:void CheckCapacity(){if (_size == _capacity){int newcapacity = _capacity * 2;DataType* temp = (DataType*)realloc(_array, newcapacity *sizeof(DataType));if (temp == NULL){perror("realloc申请空间失败!!!");return;}_array = temp;_capacity = newcapacity;}}
private:DataType* _array;int _capacity;int _size;
};
int main()
{Stack s;s.Init();s.Push(1);s.Push(2);s.Push(3);s.Push(4);printf("%d\n", s.Top());printf("%d\n", s.Size());s.Pop();s.Pop();printf("%d\n", s.Top());printf("%d\n", s.Size());s.Destroy();return 0;
}