log(3C)
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log $builtin function
Determine the natural logarithm of a number.
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Calling Sequence
double m, n, log();
m = log(n);
(or)
$builtin double log();
double m, n;
m = log(n);
Description
The log function returns the natural logarithm of a number. A
natural log is a log to the base e; e has the approximate value
2.718.
The first version noted above uses a function call. The second
might generate smaller or faster code, but may not run under
other C compilers. The include file math.h defines this entry
and uses the $builtin version.
Returns
If the log routine receives an illegal input (a zero or a
negative number), it returns -HUGE (defined in math.h) and sets
the last error (errno) to the error code ERANGE. Otherwise, it
returns the natural logarithm of the number passed to it.
You can redefine the function matherr to provide alternate error
handling.
Related Functions
See also the log10 function.
Example
/* Program test for the log() function */
#include <math.h>
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log(3C)
double atof(), m, n, log();
int i = 1;
main(argc, argv)
int argc;
char *argv[];
{
while (i < argc) {
n = atof(argv[i]);
printf("Natural log of %f is %f.\n", n, m = log(n));
i++;
}
}
A call to the program test with the numbers 2, 2.718, 10, and
1024 generates the output
Natural log of 2.000000 is 0.693147.
Natural log of 2.718000 is 0.999896.
Natural log of 10.000000 is 2.302585.
Natural log of 1024.000000 is 6.931472.
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