What is C++ std::numbers?

The C++20 standard introduced a compelling library feature, std::numbers, aimed at enriching the language’s support for mathematical constants. This addition, part of the <numbers> header, provides compile-time constants for a variety of mathematical values. These constants offer precision and ease of use that can significantly improve the readability and accuracy of mathematical computations in C++ programs.

Introduction to std::numbers

The std::numbers library is a static collection of mathematical constants with varying degrees of precision, depending on the type. It includes well-known constants such as ππ (pi), ee (Euler’s number), and many others, facilitating their use without the need for manual definition or inclusion of external libraries.

Key features and benefits

  • Precision: The constants in std::numbers are defined as constexpr and are template-specialized for different floating-point types, including float, double, and long double. This means that we can use these constants with the precision our application requires.
  • Convenience: Prior to C++20, programmers often defined these constants themselves or relied on less standardized ways of accessing them. With std::numbers, these constants are readily available and standardized across different compilers and platforms.
  • Type safety and readability: Using std::numbers enhances code readability and reduces the likelihood of errors associated with manually defining and using mathematical constants.

Available constants

The <numbers> header includes a variety of constants. Here are a few notable examples:

  • std::numbers::pi: Represents the π constant, the ratio of the circumference of a circle to its diameter.
  • std::numbers::e: Represents Euler’s number, the base of natural logarithms.
  • std::numbers::phi: Represents the golden ratio, an irrational number that appears in various aspects of art, architecture, and nature.
  • std::numbers::sqrt2: Represents the square root of 2, the length of the diagonal of a square with unit side length.

Code example

Let’s look at code example demonstrating how to use std::numbers in a C++ program:

#include <iostream>
#include <numbers>
int main() {
    std::cout << "Pi: " << std::numbers::pi << std::endl;
    std::cout << "Euler's number: " << std::numbers::e << std::endl;
    std::cout << "Golden ratio: " << std::numbers::phi << std::endl;
    std::cout << "Square root of 2: " << std::numbers::sqrt2 << std::endl;
    return 0;
}

Code explanation

  • Lines 1–2: We include two headers: <iostream> for handling input/output operations, allowing text to be printed to the console, and <numbers> for accessing pre-defined mathematical constants.

  • Line 4: We define a main function as the entry point of the program. It’s where the execution of the program begins.

  • Line 5: We utilize std::cout along with std::numbers::pi to print the value of ππ (pi) to the console. This line showcases the use of the ππ constant from the <numbers> header.

  • Line 6: Similar to the previous line, we print Euler’s number (ee) to the console using std::numbers::e. This demonstrates how to access and use Euler’s number from the <numbers> library.

  • Line 7: We print the value of the golden ratio (phiphi) using std::numbers::phi. This line highlights the availability of the golden ratio as a constant in the <numbers> header.

  • Line 8: We output the square root of 22 to the console, utilizing std::numbers::sqrt2. This is an example of accessing another mathematical constant provided by the <numbers> header.

Application

Whether we’re working on scientific simulations, graphics rendering, or any other domain where mathematical constants are essential, std::numbers is a valuable addition to our programming toolkit.

std::numbers simplifies the development of mathematically intensive applications. For C++ programmers, this means improved code readability, accuracy, and a more streamlined approach to mathematical programming. Whether we’re working on scientific simulations, graphics rendering, or any other domain where mathematical constants are essential, std::numbers is a valuable addition to our programming toolkit.

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