NAME¶

std::cbrt,std::cbrtf,std::cbrtl - std::cbrt,std::cbrtf,std::cbrtl

Synopsis¶

Defined in header <cmath>
float cbrt ( float num );

double cbrt ( double num ); (until C++23)

long double cbrt ( long double num );
/* floating-point-type */ (since C++23)
cbrt ( /* floating-point-type */ num ); (constexpr since C++26)
float cbrtf( float num ); (1) (2) (since C++11)
(constexpr since C++26)
long double cbrtl( long double num ); (3) (since C++11)
(constexpr since C++26)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer > (A) (constexpr since C++26)
double cbrt ( Integer num );

1-3) Computes the cube root of num.
The library provides overloads of std::cbrt for all cv-unqualified floating-point
types as the type of the parameter.
(since C++23)

A) Additional overloads are provided for all integer types, which are (since C++11)
treated as double.

Parameters¶

num - floating-point or integer value

Return value¶

If no errors occur, the cube root of num (\(\small{\sqrt[3]{num} }\)
3
√
num), is returned.

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.

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

* if the argument is ±0 or ±∞, it is returned, unchanged.
* if the argument is NaN, NaN is returned.

Notes¶

std::cbrt(num) is not equivalent to std::pow(num, 1.0 / 3) because the rational
number \(\small{\frac1{3} }\)

1
3

is typically not equal to 1.0 / 3 and std::pow cannot raise a negative base to a
fractional exponent. Moreover, std::cbrt(num) usually gives more accurate results
than std::pow(num, 1.0 / 3) (see example).

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::cbrt(num) has the same effect as std::cbrt(static_cast<double>(num)).

Example¶

// Run this code

#include <cmath>
#include <iomanip>
#include <iostream>
#include <limits>

int main()
{
std::cout
<< "Normal use:\n"
<< "cbrt(729) = " << std::cbrt(729) << '\n'
<< "cbrt(-0.125) = " << std::cbrt(-0.125) << '\n'
<< "Special values:\n"
<< "cbrt(-0) = " << std::cbrt(-0.0) << '\n'
<< "cbrt(+inf) = " << std::cbrt(INFINITY) << '\n'
<< "Accuracy and comparison with `pow`:\n"
<< std::setprecision(std::numeric_limits<double>::max_digits10)
<< "cbrt(343) = " << std::cbrt(343) << '\n'
<< "pow(343,1.0/3) = " << std::pow(343, 1.0 / 3) << '\n'
<< "cbrt(-343) = " << std::cbrt(-343) << '\n'
<< "pow(-343,1.0/3) = " << std::pow(-343, 1.0 / 3) << '\n';
}

Possible output:¶

Normal use:
cbrt(729) = 9
cbrt(-0.125) = -0.5
Special values:
cbrt(-0) = -0
cbrt(+inf) = inf
Accuracy and comparison with `pow`:
cbrt(343) = 7
pow(343,1.0/3) = 6.9999999999999991
cbrt(-343) = -7
pow(-343,1.0/3) = -nan

See also¶

pow
powf raises a number to the given power (\(\small{x^y}\)x^y)
powl (function)
(C++11)
(C++11)
sqrt computes square root (\(\small{\sqrt{x}}\)
sqrtf √
sqrtl x)
(C++11) (function)
(C++11)
computes square root of the sum of the squares of two
or three
(since C++17) given numbers (\(\scriptsize{\sqrt{x^2+y^2}}\)
√
hypot x2
hypotf +y2
hypotl )
(C++11) , (\(\scriptsize{\sqrt{x^2+y^2+z^2}}\)
(C++11) √
(C++11) x2
+y2
+z2
)
(since C++17)
(function)
C documentation for
cbrt