std::sqrt

From cppreference.com
< cpp‎ | numeric‎ | math
 
C++
 
Numerics library
 
Common mathematical functions
Functions
Basic operations
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)
Exponential functions
(C++11)
(C++11)
(C++11)
(C++11)
Power functions
sqrt
(C++11)
(C++11)
Trigonometric and hyperbolic functions
(C++11)
(C++11)
(C++11)
Error and gamma functions
(C++11)
(C++11)
(C++11)
(C++11)
Nearest integer floating point operations
(C++11)(C++11)(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)
Floating point manipulation functions
(C++11)(C++11)
(C++11)
(C++11)
(C++11)(C++11)
(C++11)
Classification/Comparison
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Macro constants
(C++11)(C++11)(C++11)(C++11)(C++11)
 
Defined in header <cmath>
float       sqrt( float arg );
 (1)
double      sqrt( double arg );
 (2)
long double sqrt( long double arg );
 (3)
double      sqrt( Integral arg );
 (4) (since C++11)

Computes the square root of arg.

4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to 2) (the argument is cast to double).

Parameters

arg - Value of a floating-point or Integral type

Return value

If no errors occur, square root of arg (√arg), is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported)

If a range error occurs due to underflow, the correct result (after rounding) is returned.

Error handling

Errors are reported as specified in math_errhandling

Domain error occurs if arg is less than zero.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

  • If the argument is less than -0, FE_INVALID is raised and NaN is returned.
  • If the argument is +∞ or ±0, it is returned, unmodified.
  • If the argument is NaN, NaN is returned

Notes

std::sqrt is required by the IEEE standard to be exact. The only other operations required to be exact are the arithmetic operators and the function std::fma. After rounding to the return type (using default rounding mode), the result of std::sqrt is indistinguishable from the infinitely precise result. In other words, the error is less than 0.5 ulp. Other functions, including std::pow, are not so constrained.

Example

Run this code
#include <iostream>
#include <cmath>
#include <cerrno>
#include <cfenv>
#include <cstring>
 
#pragma STDC FENV_ACCESS ON
 
int main()
{
    // normal use
    std::cout << "sqrt(100) = " << std::sqrt(100) << '\n'
              << "sqrt(2) = " << std::sqrt(2) << '\n'
              << "golden ratio = " << (1+std::sqrt(5))/2 << '\n';
    // special values
    std::cout << "sqrt(-0) = " << std::sqrt(-0.0) << '\n';
    // error handling
    errno = 0; std::feclearexcept(FE_ALL_EXCEPT);
    std::cout << "sqrt(-1.0) = " << std::sqrt(-1) << '\n';
    if(errno == EDOM)
        std::cout << "    errno = EDOM " << std::strerror(errno) << '\n';
    if(std::fetestexcept(FE_INVALID))
        std::cout << "    FE_INVALID raised\n";
}

Possible output: 

sqrt(100) = 10
sqrt(2) = 1.41421
golden ratio = 1.61803
sqrt(-0) = -0
sqrt(-1.0) = -nan
    errno = EDOM Numerical argument out of domain
    FE_INVALID raised

See also

 raises a number to the given power (xy)
(function)
(C++11)
 computes cubic root (3√x)
(function)
(C++11)
 computes square root of the sum of the squares of two given numbers (√x2
+y2
)
(function)
complex square root in the range of the right half-plane
(function template)
applies the function std::sqrt to each element of valarray
(function template)
C documentation for sqrt
Retrieved from "http://en.cppreference.com/mwiki/index.php?title=cpp/numeric/math/sqrt&oldid=90516"