# exp(), expf(), expl()

Compute the exponential function of a number

## Synopsis:

```#include <math.h>

double exp( double x );

float expf( float x );

long double expl( long double x );
```

## Arguments:

x
The number for which you want to calculate the exponential.

## Library:

libm

Use the -l m option to qcc to link against this library.

## Description:

These functions compute the exponential function of x (i.e., ex).

To check for error situations, use feclearexcept() and fetestexcept(). For example:

• Call feclearexcept(FE_ALL_EXCEPT) before calling exp(), expf(), or expl().
• On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

## Returns:

The exponential value of x.

If x is: These functions return: Errors:
±0.0 1
A value that would cause overflow Inf FE_OVERFLOW
A value that would cause underflow 0.0 FE_UNDERFLOW
-Inf 0.0
Inf Inf
NaN NaN

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

## Examples:

```#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
int except_flags;

feclearexcept(FE_ALL_EXCEPT);

printf( "%f\n", exp(.5) );

except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

return EXIT_SUCCESS;
}
```

produces the output:

```1.648721
```

## Classification:

Safety:
Cancellation point No
Interrupt handler No
Signal handler No