sizeof()

sizeof()用于查询结构体或实例的内存分配大小(在内存中占有的字节)，单位字节，eg：

#include <iostream>
using namespace std;

class Girl
{
private:
    int age;
    char name[4];
};
struct Pointer
{
   int X;
   int Y;    
} p;

int main(int argc, char const *argv[])
{
    int a = 1;
    int *p =&a;
    char b = 'X';
    char *c = &b;
    cout<<"int a:"<<sizeof(a)<<endl;
    cout<<"int *p:"<<sizeof(p)<<endl;
    cout<<"char b:"<<sizeof(b)<<endl;
    cout<<"char *c:"<<sizeof(c)<<endl;
    cout<<"Girl:"<<sizeof(Girl)<<endl;
    cout<<"struct Pointer:"<<sizeof(p)<<endl;
    return 0;
}

int a:4
int *p:8
char b:1
char *c:8
Girl:8
struct Pointer:8

可以看到指针的大小与数据类型有关，后面我们还会学到指针的偏移量其实偏移的是n个数据类型