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log, logl

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

Copy Code

    #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 |  | + | + | +

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