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Showing content from https://cplusplus.com/reference/cmath/expm1/ below:

function

expm1

     double expm1  (double x);      float expm1f (float x);long double expm1l (long double x);

     double expm1 (double x);      float expm1 (float x);long double expm1 (long double x);     double expm1 (T x);           // additional overloads for integral types

Compute exponential minus one

Returns e raised to the power x minus one: e^x-1.

For small magnitude values of x, expm1 may be more accurate than exp(x)-1.

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 of the exponent.

Return Valuee raised to the power of x, minus one.
If the magnitude of the result is too large to be represented by a value of the return type, the function returns HUGE_VAL (or HUGE_VALF or HUGE_VALL) with the proper sign, and an overflow range error occurs:

If an overflow range 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_OVERFLOW is raised.

Example

/* expm1 example */
#include <stdio.h>      /* printf */
#include <math.h>       /* expm1 */

int main ()
{
  double param, result;
  param = 1.0;
  result = expm1 (param);
  printf ("expm1 (%f) = %f.\n", param, result );
  return 0;
}

Output:

expm1 (1.000000) = 1.718282.