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Showing content from https://cplusplus.com/reference/cmath/logb/ below:

function

logb

     double logb  (double x);      float logbf (float x);long double logbl (long double x);

     double logb (double x);      float logb (float x);long double logb (long double x);     double logb (T x);           // additional overloads for integral types

Compute floating-point base logarithm

Returns the logarithm of |x|, using FLT_RADIX as base for the logarithm.

On most platforms, FLT_RADIX is 2, and thus this function is equivalent to log2 for positive values.

Header

<tgmath.h>

provides a type-generic macro version of this function.

Additional overloads

are provided in this header (

<cmath>

) for the

integral types

: These overloads effectively cast

to a

double

before calculations (defined for

being any

integral type

Parameters

x: Value whose logarithm is calculated.

Return Value The base-FLT_RADIX logarithm of x.
If x is zero it may cause a domain error or a pole error (or no error, depending on the library implementation).

If an domain error occurs:

- And math_errhandling has MATH_ERRNO set: the global variable errno is set to EDOM.
- And math_errhandling has MATH_ERREXCEPT set: FE_INVALID is raised.

If a pole error occurs:

- And math_errhandling has MATH_ERRNO set: the global variable errno is set to ERANGE.
- And math_errhandling has MATH_ERREXCEPT set: FE_DIVBYZERO is raised.

Example

/* logb example */
#include <stdio.h>      /* printf */
#include <math.h>       /* logb */

int main ()
{
  double param, result;
  param = 1024.0;
  result = logb (param);
  printf ("logb (%f) = %f.\n", param, result );
  return 0;
}

Output:

logb (1024.000000) = 10.000000