std::stod, std::stof, std::stold in C++

C++ is one of its kinds of powerful programming language that has an extensive Standard Library providing effective solutions for many operations. Commonly, string conversion to floating point numbers while dealing with numeric data. The C++ Standard Library provides three essential functions for this purpose: std::stod, std::stof, and std::stold. It is a complete guide that will explain these functions and include some codes for examples as well as their output.

Understanding the Basics:

std::stod

The std::stod converts a string to a double precision floating point number. It is particularly relevant in cases where high precision must be observed with respect to numeric values. Let's dive into a simple example:

#include <iostream>
#include <string>
 
int main() {
    std::string str = "3.14";
    double result = std::stod(str);
 
    std::cout << "String: " << str << "\n";
    std::cout << "Double: " << result << "\n";
 
    return 0;
}

Output:

String: 3.14
Double: 3.14

std::stof

The std::stof function looks like the std::stod, but it converts the string to a single precision float. If you are working in an environment where precision is not as critical, using std: stöf could also prove more memory efficient as well. Let's illustrate this with an example:

#include <iostream>
#include <string>
 
int main() {
    std::string str = "2.718";
    float result = std::stof(str);
 
    std::cout << "String: " << str << "\n";
    std::cout << "Float: " << result << "\n";
 
    return 0;
}

Output:

String: 2.718
Float: 2.718

std::stold

The std::stold functions are intended under situations when precision needs to hit even a higher level, and the type of the target is long double. Let's explore an example:

#include <iostream>
#include <string>
 
int main() {
    std::string str = "12345678901234567890.12345678901234567890";
    long double result = std::stold(str);
 
    std::cout << "String: " << str << "\n";
    std::cout << "Long Double: " << result << "\n";
 
    return 0;
}

Output:

String: 12345678901234567890.12345678901234567890
Long Double: 1.23457e+019

Advanced Usage:

However, these conversion functions do not deal with simple converting of strings into numeric form only. These products are also featured with other things such that they improve on their adaptability and toughness.

Handling Invalid Input:

Any useful conversion function should be able to cope with invalid data. The conversion functions throw a std::invalid_argument will result in a exception if the conversion is not possible. If you want to handle this, you can use a try-catch block:

#include <iostream>
#include <string>
 
int main() {
    std::string invalidStr = "invalid";
 
    try {
        double result = std::stod(invalidStr);
        std::cout << "Result: " << result << "\n";
    } catch (const std::invalid_argument& e) {
        std::cerr << "Error: " << e.what() << "\n";
    }
 
    return 0;
}

Output:

Error: stod

Explanation:

Here, "stod" is the description of the exception thrown, indicating that the error occurred during the conversion using std::stod. However, the exact error message might depend on the C++ implementation and the underlying platform, but it normally outlines the type of the error.

Using std::size_t:

When converting to an unsigned integer type of std::size_t, the function may use the std::stoul function. It is especially useful when dealing with string lengths or indices:

Example:

#include <iostream>
#include <string>
 
int main() {
    std::string str = "42";
    std::size_t result = std::stoul(str);
 
    std::cout << "String: " << str << "\n";
    std::cout << "std::size_t: " << result << "\n";
 
    return 0;
}

Output:

String: 42
std::size_t: 42

Explanation:

Here, the original string "42" is printed, and the result of the conversion is also printed, showing that the string "42" has been successfully converted to the corresponding std::size_t that contains a value of 42.

Conclusion:

In conclusion, proper understanding of string to numeric conversion in C++ is paramount in building strong and error free programming solutions. The exploration of std::stod, std::stof, and std::stold through provides an understanding of converted strings to double, float, and long double respectively. These functions operate on a variety of precise levels, which are useful when integrating numeric needs at multiple points. The advanced features, such as handling invalid input and utilizing std::size_t from std::stoul for broader applicability of the conversion functions. These functions serve as the basic means employed across the C++ Standard in converting strings to numbers, helping developers develop strong programs devoid of errors.

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