log, logl

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Header File

math.h

Category

Math Routines

Prototype

double log(double x);

long double logl(long double x);

Description

Calculates the natural logarithm of x.

log calculates the natural logarithm of x.

logl is the long double version; it takes a long double argument and returns a long double result.

Return Value

On success, log and logl return the value calculated, ln(x).

errno

EDOM	Domain error

If x is 0, the functions return the value negative HUGE_VAL (log) or negative _LHUGE_VAL (logl), and set errno to ERANGE. Error handling for these routines can be modified through the functions _matherr and _matherrl.

Example

#include <math.h>
#include <stdio.h>
int main(void)
{
   double result;
   double x = 8.6872;
   result = log(x);
   printf("The natural log of %lf is %lf\n", x, result);
   return 0;
}

Portability

	POSIX	Win32	ANSI C	ANSI C++
log	+	+	+	+
logl		+	+	+