string st1("Hello world!");
string *ps = &st1;
cout << sizeof(ps); // 输出：4
cout << sizeof(*ps); // 输出：16
但是第二句也有人运行出了4

一个string 的大小与它所指的字符串的长度无关，都是28,as就是28*4=112,as[0]就是28;
sizeof操作符应用在char类型上时，在所有的C++实现中结果都是1,所以sizeof('a') 是1;
"a"未声明为string类型，由'a' 和一个结束符组成，所以是2.

#include "iostream.h"
#include <string>
using namespace std;

void main()
{
 string as[4] = {"a","light","drizzle","was"};
 cout<<sizeof(as)<<endl<<sizeof(as[0])<<endl<<sizeof(string)<<endl
  <<sizeof("a")<<endl<<sizeof('a')<<endl;
}

Impelentation and performance characteristics of string are not
standardized. g++ probably uses a ref-counted string implementation
with 'copy-on-write' whereas Microsoft/Dinkumware uses SSO (small
string optimization) with an internal buffer resulting in cheap
creation and copying for 'short' strings but expensive copying for
'long' strings.