function
<cmath> <ctgmath>

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: ex-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 x to a double before calculations (defined for T being any integral type).

Parameters

x
Value of the exponent.

Return Value

e 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

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/* 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.

See also

exp
Compute exponential function (function )
log1p
Compute logarithm plus one (function )
pow
Raise to power (function )

C++