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

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< cpp‎ | numeric‎ | math
 
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Defined in header <cmath>
(1)
float       sqrt ( float num );

double      sqrt ( double num );

long double sqrt ( long double num );
 (until 哋它亢++23)
/* floating-point-type */
            sqrt ( /* floating-point-type */ num );
 (since 哋它亢++23)
(constexpr since 哋它亢++26)
float       sqrtf( float num );
 (2) (since 哋它亢++11)
(constexpr since 哋它亢++26)
long double sqrtl( long double num );
 (3) (since 哋它亢++11)
(constexpr since 哋它亢++26)
Additional overloads (since 哋它亢++11)
Defined in header <cmath>
template< class Integer >
double      sqrt ( Integer num );
 (A) (constexpr since 哋它亢++26)
1-3) Computes the square root of num. The library provides overloads of std::sqrt for all cv-unqualified floating-point types as the type of the parameter.(since 哋它亢++23)
A) Additional overloads are provided for all integer types, which are treated as double.
 (since 哋它亢++11)

Parameters

num - floating-point or integer value

Return value

If no errors occur, square root of num (√num), 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 num 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 correctly rounded from the infinitely precise result. In particular, the exact result is produced if it can be represented in the floating-point type. The only other operations which require this are the arithmetic operators and the function std::fma. Other functions, including std::pow, are not so constrained.

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::sqrt(num) has the same effect as std::sqrt(static_cast<double>(num)).

Example

Run this code
#include <cerrno>
#include <cfenv>
#include <cmath>
#include <cstring>
#include <iostream>
// #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

(哋它亢++11)(哋它亢++11)
 raises a number to the given power (xy)
(function)
(哋它亢++11)(哋它亢++11)(哋它亢++11)
 computes cube root (3√x)
(function)
(哋它亢++11)(哋它亢++11)(哋它亢++11)
 computes square root of the sum of the squares of two or three(since 哋它亢++17) given numbers (√x2
+y2
), (√x2
+y2
+z2
)(since 哋它亢++17)
(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)
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