std::stoul and std::stoull in C++

std::stoul

Convert string to unsigned integer. Parses str interpreting its content as an integral number of the specified base, which is returned as an unsigned long value.

unsigned long stoul 
(const string&  str, size_t* idx = 0, int base = 10);
Parameters :
str : String object with the 
representation of an integral number.
idx : Pointer to an object of type size_t, 
whose value is set by the function to position of the 
next character in str after the numerical value.
This parameter can also be a null pointer, in which case
it is not used.
base : Numerical base (radix) that determines
the valid characters and their interpretation.
If this is 0, the base used is determined by the format in
the sequence.Notice that by default this argument is 10, not 0. 

std::stoull

Convert string to unsigned long long. Parses str interpreting its content as an integral number of the specified base, which is returned as a value of type unsigned long long.

unsigned long long stoull 
(const string&  str, size_t* idx = 0, int base = 10);
Parameters :
str : String object with the representation 
of an integral number.
idx : Pointer to an object of type size_t,
whose value is set by the function to position of the next 
character in str after the numerical value. This parameter can 
also be a null pointer, in which case it is not used.
base : Numerical base (radix) that determines 
the valid characters and their interpretation.
If this is 0, the base used is determined by the format in the
sequence. Notice that by default this argument is 10, not 0. 

Examples:

Input : FF
Output : 255

Input : FFFFF
Output : 

// CPP code to convert hexadecimal
// string to int
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Hexadecimal string
    string str = "FF";

    // Converted integer
    unsigned long num = stoul(str, nullptr, 16);

    // Printing the integer
    cout << num << "\n";

    // Hexadecimal string
    string st = "FFFFFF";

    // Converted long long
    unsigned long long val = stoull(st, nullptr, 16);

    // Printing the long long
    cout << val;
    return 0;
}

Output:

255
16777215

Another Example : Program to compare two strings containing hexadecimal values
Here stoul is used, but in cases of numbers exceeding unsigned long value, stoull is used.

// CPP code to compare two
// hexadecimal string
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Hexadecimal string
    string s1 = "4F";
    string s2 = "A0";

    // Converted integer
    unsigned long n1 = stoul(s1, nullptr, 16);
    unsigned long n2 = stoul(s2, nullptr, 16);

    // Compare both string
    if (n1 > n2)
        cout << s1 << " is greater than " << s2;
    else if (n2 > n1)
        cout << s2 << " is greater than " << s1;
    else
        cout << "Both " << s1 << " and " << s2 << " are equal";
    return 0;
}

Output:

A0 is greater than 4F