The compare function of the C++ STL string class uses

#include <iostream>
#include <string>
using namespace std;

intmain()
{
    string a("aBcdef");
    string b("AbcdEf");
    string c("123456");
    string d("123dfg");
    //The following are various comparison methods
    //Subtract the following ASCII code from the front, >0 returns 1, <0 returns -1, the same returns 0
    //Completely compare a and b
    int m=a.compare(b);
    //Comparison of "Bcdef" and "AbcdEf", comparing bits 1 to 5 of a and b
    int n=a.compare(1,5,b);
    //Comparison of "Bcdef" and "Ef"
    int p=a.compare(1,5,b,4,2);
    //Comparison of "123" and "123"
    int q=c.compare(0,3,d,0,3);
    cout<<"m="<<m<<",n="<<n<<",p="<<p<<",q="<<q<<endl;
    return 0;
}