C++ String::stoll() function

The C++ std::string::stoll() function is used to convert a string to a long long integer. It is used to analyse numerical values from strings and handle large integers. This function takes two optional parameters: pos( to specify the starting position in the string) and base (to define the number base, such as decimal or hexadecimal).

Syntax

Following is the syntax for std::string::stoll() function.

long long stoll (const string&  str, size_t* idx = 0, int base = 10);long long stoll (const wstring& str, size_t* idx = 0, int base = 10);

Parameters

• str − It indicates the string object with the representation of a integral number.
• idx − It indicates the 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.
• base − It indicates the numerical base that determines the valid character and their interpretation.

Return value

It returns a string as the value into a long long integer.

Example 1

Following is the basic example to convert a string into a long long integer using C++.

#include <iostream>
#include <string>
using namespace std;
int main() {
   string str = "9223372036854775807";
   long long int number = stoll(str);
   cout << number << endl;
   return 0;
}

Output

If we run the above code it will generate the following output.

9223372036854775807

Example 2

In this example, we are passing a hexadecimal string to convert into a long int.

#include <iostream>
#include <string>
using namespace std;
int main() {
   string hexStr = "7FFFFFFFFFFFFFFF";
   long long number = stoll(hexStr, nullptr, 16);
   cout << number << endl;
   return 0;
}

Output

If we run the above code it will generate the following output.

 9223372036854775807

Example 3

In this program we are giving comment-line argument conversion to long long integer.

#include <iostream>
#include <string>
using namespace std;
int main(int argc, char * argv[]) {
   if (argc != 2) {
      cerr << "Usage: " << argv[0] << " <number>" << endl;
      return 1;
   }
   try {
      string argStr = argv[1];
      long long number = stoll(argStr);
      cout << "The command-line argument \"" << argStr << "\" converted to long long is " << number << endl;
   } catch (const std::exception & e) {
      cerr << "Error: " << e.what() << endl;
      return 1;
   }
   return 0;
}

Output

Following is the output of the above code.

Usage: main <number>