cbrt, cbrtf, cbrtl - cppreference.com (original) (raw)

Defined in header <math.h>
float cbrtf( float arg ); (1) (since C99)
double cbrt( double arg ); (2) (since C99)
long double cbrtl( long double arg ); (3) (since C99)
Defined in header <tgmath.h>
#define cbrt( arg ) (4) (since C99)

1-3) Computes the cube root of arg.

  1. Type-generic macro: If arg has type long double, cbrtl is called. Otherwise, if arg has integer type or the type double, cbrt is called. Otherwise, cbrtf is called.

Contents

[edit] Parameters

arg - floating-point value

[edit] Return value

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

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

[edit] Error handling

Errors are reported as specified in math_errhandling.

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

[edit] Notes

cbrt(arg) is not equivalent to pow(arg, 1.0/3) because the rational number \(\small{\frac1{3} }\) is typically not equal to 1.0/3 and std::pow cannot raise a negative base to a fractional exponent. Moreover, cbrt(arg) usually gives more accurate results than pow(arg, 1.0/3) (see example).

[edit] Example

#include <float.h> #include <math.h> #include <stdio.h>   int main(void) { printf("Normal use:\n" "cbrt(729) = %f\n", cbrt(729)); printf("cbrt(-0.125) = %f\n", cbrt(-0.125)); printf("Special values:\n" "cbrt(-0) = %f\n", cbrt(-0.0)); printf("cbrt(+inf) = %f\n", cbrt(INFINITY)); printf("Accuracy:\n" "cbrt(343) = %.*f\n", DBL_DECIMAL_DIG, cbrt(343)); printf("pow(343,1.0/3) = %.*f\n", DBL_DECIMAL_DIG, pow(343, 1.0/3)); }

Possible output:

Normal use: cbrt(729) = 9.000000 cbrt(-0.125) = -0.500000 Special values: cbrt(-0) = -0.000000 cbrt(+inf) = inf Accuracy: cbrt(343) = 7.00000000000000000 pow(343,1.0/3) = 6.99999999999999911

[edit] References

[edit] See also