C++ string stoll Function

C++ String stoll

The std::stoll function in C++ converts a string representation of a signed integral number into a long long. It is part of the C++11 standard and is defined in the <string> header. This function is generally used for parsing strings containing large numerical values, such as those read from files or user input.

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Syntax of string stoll function

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

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Parameters of string stoll function

Parameter	Description
str	The string containing the representation of a signed integral number.
idx (optional)	A pointer to a std::size_t object. If provided, it is set to the position of the first character in str after the numerical value. Defaults to 0.
base (optional)	The numerical base (radix) for the conversion, which can range from 2 to 36. If set to 0, the base is automatically deduced from the string format (e.g., prefixes like 0x indicate base 16). Defaults to 10.

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Return Value of string stoll function

On successful conversion, std::stoll returns the converted value as a long long. If the conversion fails, it throws an exception.

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Exceptions for string stoll function

The std::stoll function can throw the following exceptions:

• std::invalid_argument: Thrown if the input string does not contain a valid signed integral number.
• std::out_of_range: Thrown if the converted value exceeds the range of the long long type.

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Examples for string stoll function

Example 1: Converting a Decimal String to Long Long

In this example, we convert a string containing a decimal number to a long long using std::stoll.

Program

#include 
#include 

int main() {
    std::string str = "9223372036854775807"; // Maximum value for long long
    long long num = std::stoll(str);
    std::cout << "The long long value is: " << num << std::endl;
    return 0;
}

Output

The long long value is: 9223372036854775807

Explanation

1. The program includes the necessary headers: for input and output operations, and for string handling.
2. A string str is initialized with the value "9223372036854775807", which is the maximum value for a long long.
3. The std::stoll function converts the string to a long long and stores it in the variable num.
4. The program outputs the long long value using std::cout.

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Example 2: Converting a Hexadecimal String to Long Long

In this example, we convert a string representing a hexadecimal number to a long long by specifying the base as 16.

Program

#include 
#include 

int main() {
    std::string str = "0x7FFFFFFFFFFFFFFF"; // Maximum value for long long in hexadecimal
    long long num = std::stoll(str, nullptr, 16);
    std::cout << "The long long value is: " << num << std::endl;
    return 0;
}

Output

The long long value is: 9223372036854775807

Explanation

1. The string str contains the hexadecimal representation of the maximum long long value.
2. The std::stoll function is called with the base parameter set to 16, converting the hexadecimal string to a decimal long long.
3. The resulting long long value is stored in num and printed using std::cout.

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Examples for Exception Handling in stoll

Example 1: Handling std::invalid_argument

This exception is thrown when the string does not contain a valid numeric representation.

Program

#include 
#include 
#include 

int main() {
    try {
        std::string invalidStr = "HelloWorld";
        long long num = std::stoll(invalidStr);
    } catch (const std::invalid_argument& e) {
        std::cout << "Invalid argument exception: " << e.what() << std::endl;
    }
    return 0;
}

Output

Invalid argument exception: stoll

Explanation

1. The string invalidStr contains non-numeric characters, making it an invalid input.
2. When std::stoll is called, it throws a std::invalid_argument exception.
3. The exception is caught in the catch block, and an appropriate error message is displayed.

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Example 2: Handling std::out_of_range

This exception is thrown when the value represented by the string exceeds the range of the long long type.

Program

#include 
#include 
#include 

int main() {
    try {
        std::string largeStr = "99999999999999999999";
        long long num = std::stoll(largeStr);
    } catch (const std::out_of_range& e) {
        std::cout << "Out of range exception: " << e.what() << std::endl;
    }
    return 0;
}

Output

Out of range exception: stoll

Explanation

1. The string largeStr contains a value that exceeds the range of a long long.
2. When std::stoll attempts to convert the string, it throws a std::out_of_range exception.
3. The exception is caught in the catch block, and an appropriate error message is displayed.