C Language and Libraries Help (clang.hlp) (Table of Contents; Topic list)
Logarithmic Functions
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─────Run-Time Library───────────────────────────────────────────────────────
 
  Include:   <math.h>, <errno.h>
 
  Syntax:    double log( double x );
             double log10( double x );
             long double _logl( long double x );
             long double _log10l( long double x );
 
  Returns:   the logarithm of <x> if successful; -HUGE_VAL (or
             -_LHUGE_VAL for the long double functions) if not.
             errno: EDOM (if <x> is less than 0)
                    ERANGE (if <x> is equal to 0)
 
  See also:  exp, ldexp, frexp, pow, sqrt, _matherr
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