# expf (3p) - Linux Manuals

## expf: exponential function

## PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.## NAME

exp, expf, expl - exponential function

## SYNOPSIS

**#include <math.h>
**

**
double exp(double** *x***);
float expf(float**

*x*

**);**

long double expl(long double

long double expl(long double

*x*

**);**

## DESCRIPTION

These functions shall compute the base- *e* exponential of *x*.

An application wishing to check for error situations should set *errno*
to zero and call
*feclearexcept*(FE_ALL_EXCEPT) before calling these functions.
On return, if *errno* is non-zero or
*fetestexcept*(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.

## RETURN VALUE

Upon successful completion, these functions shall return the exponential
value of *x*.

If the correct value would cause overflow, a range error shall occur
and *exp*(), *expf*(), and *expl*() shall
return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL,
respectively.

If the correct value would cause underflow, and is not representable, a range error may occur, and either 0.0 (if supported), or an implementation-defined value shall be returned.

If
*x* is NaN, a NaN shall be returned.

If *x* is ±0, 1 shall be returned.

If *x* is -Inf, +0 shall be returned.

If *x* is +Inf, *x* shall be returned.

If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be returned.

## ERRORS

These functions shall fail if:

- Range Error
- The result overflows.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then *errno* shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the overflow floating-point exception shall be
raised.

These functions may fail if:

- Range Error
- The result underflows.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then *errno* shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the underflow floating-point exception shall be
raised.

*The following sections are informative.*

## EXAMPLES

## APPLICATION USAGE

Note that for IEEE Std 754-1985 **double**, 709.8 < *x* implies
*exp*( *x*) has overflowed. The
value *x* < *exp*( *x*) has underflowed.

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

## RATIONALE

## FUTURE DIRECTIONS

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

## SEE ALSO

*feclearexcept*(), *fetestexcept*(), *isnan*(), *log*(),
the Base Definitions volume of
IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions
for
Mathematical Functions, *<math.h>*