return value of the function capacity and max_size

[summerqu]

`#include
#include
using namespace std;

int main(int argc, char const *argv[])
{
string t(10, 'a');
string a("ABC");
cout << t << " capacity : " << t.capacity() <<" max_size :"<< t.max_size()<< endl;
cout << a << " capacity : " << a.capacity() <<" max_size :"<< a.max_size()<< endl;
return 0;
}`

the result is :
aaaaaaaaaa capacity : 15 max_size :9223372036854775807
ABC capacity : 15 max_size :9223372036854775807

Is the return value of the function capacity and max_size fixed ?
if not, decide by what ?