std::sqrt, std::sqrtf, std::sqrtl

Defined in header `<cmath>`
	(1)
float sqrt ( float arg );
float sqrtf( float arg );			(since C++11)
double sqrt ( double arg );		(2)
		(3)
long double sqrt ( long double arg );
long double sqrtl( long double arg );				(since C++11)
double sqrt ( IntegralType arg );			(4)	(since C++11)

1-3) 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 (${\small \sqrt{arg} }$ $\sqrt arg$ ), 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

powpowfpowl (C++11)(C++11)	raises a number to the given power ($\small{x^y}$ $x y$ ) (function)
cbrtcbrtfcbrtl (C++11)(C++11)(C++11)	computes cubic root ($\small{\sqrt[3]{x} }$ $3 \sqrt x$ ) (function)
hypothypotfhypotl (C++11)(C++11)(C++11)	computes square root of the sum of the squares of two or three (C++17) given numbers ($\scriptsize{\sqrt{x^2+y^2} }$ $\sqrt x 2 +y 2$ ), ($\scriptsize{\sqrt{x^2+y^2+z^2} }$ $\sqrt x 2 +y 2 +z 2$ ) (function)
sqrt(std::complex)	complex square root in the range of the right half-plane (function template)
sqrt(std::valarray)	applies the function std::sqrt to each element of valarray (function template)

Compiler support
Freestanding and hosted
Language
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Technical specifications
Symbols index
External libraries

Common mathematical functions
Mathematical special functions (C++17)
Mathematical constants (C++20)
Floating-point environment (C++11)
Complex numbers
Numeric arrays
Pseudo-random number generation
Factor operations
gcd (C++17)
lcm (C++17)
Interpolations
midpoint (C++20)
lerp (C++20)
Generic numeric operations
iota (C++11)
ranges::iota (C++23)
accumulate
inner_product
adjacent_difference
partial_sum
reduce (C++17)
transform_reduce (C++17)
inclusive_scan (C++17)
exclusive_scan (C++17)
transform_inclusive_scan (C++17)
transform_exclusive_scan (C++17)
Bit operations
bit_cast (C++20)
byteswap (C++23)
has_single_bit (C++20)
bit_ceil (C++20)
bit_floor (C++20)
bit_width (C++20)
rotl (C++20)
rotr (C++20)
countl_zero (C++20)
countl_one (C++20)
countr_zero (C++20)
countr_one (C++20)
popcount (C++20)
endian (C++20)