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c99 [flag... ]file... -lm[library... ] #include <math.h>

**double log**(**double ***x*);

**float logf**(**float ***x*);

**long double logl**(**long double ***x*);

These functions compute the natural logarithm of their argument *x*, log*e*(*x*).

Upon successful completion, **log()** returns the natural logarithm of *x*.

If *x* is ±0, a pole error occurs and **log()**, **logf()**, and **logl()** return -**HUGE_VAL**, -**HUGE_VALF**, and -**HUGE_VALL**, respectively.

For finite values of *x* that are less than 0, or if *x* is -Inf, a domain error occurs and a NaN is returned.

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

If *x* is 1, +0 is returned.

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

For exceptional cases, **matherr**(3M) tabulates the values to be returned by **log()** as specified by SVID3 and XPG3.

These functions will fail if:

**Domain Error**
The finite value of *x* is negative, or *x* is -Inf.

If the integer expression (**math_errhandling** & **MATH_ERREXCEPT**) is non-zero, the invalid floating-point exception is raised.

The **log()** function sets **errno** to **EDOM** if the value of *x* is negative.

**Pole Error**
The value of *x* is 0.

If the integer expression (**math_errhandling** & **MATH_ERREXCEPT**) is non-zero, the divide-by-zero floating-point exception is raised.

An application wanting to check for exceptions should call **feclearexcept**(**FE_ALL_EXCEPT**) before calling these functions. On return, if **fetestexcept**(**FE_INVALID** | **FE_DIVBYZERO** | **FE_OVERFLOW**
| **FE_UNDERFLOW**) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

An application can also set **errno** to 0 before calling **log()**. On return, if **errno** is non-zero, an error has occurred. The **logf()** and **logl()** functions do not set **errno**.

See **attributes**(5) for descriptions of the following attributes:

ATTRIBUTE TYPE | ATTRIBUTE VALUE |

Interface Stability | Standard |

MT-Level | MT-Safe |

**exp**(3M), **feclearexcept**(3M), **fetestexcept**(3M), **isnan**(3M), **log10**(3M), **log1p**(3M), **math.h**(3HEAD), **matherr**(3M), **attributes**(5), **standards**(5)

- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- ERRORS
- USAGE
- ATTRIBUTES
- SEE ALSO

This document was created by man2html, using the manual pages.

Time: 02:39:32 GMT, October 02, 2010