c++ string 最大长度

#include <iostream>
#include <string>

using namespace std;

int main ()
{
    string s="";
    unsigned long long a=0;
    a = ~a;
    unsigned int b = 0;
    b = ~b;

    cout<<s.max_size()<<endl;
    cout<<a<<endl;
    cout<<b<<endl;
    return 0;
}

4611686018427387903
18446744073709551615
4294967295

分别是：

2^61 即 62个1

2^63 即 64个1

2^31 即 32个1