std::string::compare() in C++

Syntax 1: Compares the string *this with the string str.
int string::compare (const string& str) const
Returns:
0 : if both strings are equal.
A value < 0 : if *this is shorter than str or,
first character that doesn't match is smaller than str.
A value > 0 : if *this is longer than str or,
first character that doesn't match is greater

// CPP code for demonstrating
// string::compare (const string& str) const

#include<iostream>
using namespace std;

void compareOperation(string s1, string s2)
{
    // returns a value < 0 (s1 is smaller then s2)
    if((s1.compare(s2)) < 0)
        cout << s1 << " is smaller than " << s2 << endl;

    // returns 0(s1, is being comapared to itself)
    if((s1.compare(s1)) == 0)
        cout << s1 << " is equal to " << s1 << endl;
    else
        cout << "Strings didn't match ";
    
}

// Driver Code
int main()
{
    string s1("Geeks");
    string s2("forGeeks");
    compareOperation(s1, s2);
    
    return 0;
}

output:

Geeks is smaller than forGeeks
Geeks is equal to Geeks

Syntax 2: Compares at most, len characters of string *this, starting with index idx with the string str.

// CPP code to demonstrate
// int string::compare (size_type idx, size_type len,
// const string& str) const

#include<iostream>
using namespace std;

void compareOperation(string s1, string s2)
{
    // Compares 5 characters from index number 3 of s2 with s1
    if((s2.compare(3, 5, s1)) == 0)
        cout << "Here, "<< s1 << " are " << s2;

    else
        cout << "Strings didn't match ";
}
// Driver Code
int main()
{
    string s1("Geeks");
    string s2("forGeeks");
    compareOperation(s1, s2);
    
return 0;
}

output:

Here, Geeks are forGeeks

Syntax 3: Compares at most, len characters of string *this starting with index idx with at most, str_len characters of string str starting with index str_idx.

int string::compare (size_type idx, size_type len, const string& 
str, size_type str_idx, size_type str_len) const
Throws out_of_range if idx > size().
Throws out_of_range if str_idx > str.size().

// CPP code to demonstrate
// int string::compare (size_type idx, size_type len, const string&
// str, size_type str_idx, size_type str_len) const

#include<iostream>
using namespace std;

void compareOperation(string s1, string s2)
{
    // Compares 5 characters from index number 0 of s1 with
    // 5 characters from index 3 of s2
    if((s1.compare(0, 5, s2, 3, 5)) == 0)
        cout << "Welcome to " << s1 << s2 << " World";

    else
        cout << "Strings didn't match ";
}
// Driver Code
int main()
{
    string s1("Geeks");
    string s2("forGeeks");
    compareOperation(s1, s2);
    
return 0;
}

Output:

Welcome, to GeeksforGeeks World

from:https://www.geeksforgeeks.org/stdstringcompare-in-c/