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NAME

       log10, log10f, log10l - base 10 logarithm function

SYNOPSIS

       #include <math.h>

       double log10(double x);
       float log10f(float x);
       long double log10l(long double x);

DESCRIPTION

       These  functions  shall compute the base 10 logarithm of their argument
       x, log_10(x).

       An application wishing to check for error situations should  set  errno
       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
       functions.  On return, if errno is non-zero or  fetestexcept(FE_INVALID
       |  FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
       occurred.

RETURN VALUE

       Upon successful completion, these functions shall return  the  base  10
       logarithm of x.

       If  x  is  ±0,  a  pole  error  shall  occur and log10(), log10f(), and
       log10l()  shall   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 shall occur, and    either a NaN (if supported),  or    an
       implementation-defined value shall be returned.

       If x is NaN, a NaN shall be returned.

       If x is 1, +0 shall be returned.

       If x is +Inf, +Inf shall be returned.

ERRORS

       These functions shall fail if:

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

       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
       then  errno  shall  be  set  to  [EDOM].  If  the  integer   expression
       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero,  then  the invalid
       floating-point exception shall be raised.

       Pole Error
              The value of x is zero.

       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
       then  errno  shall  be  set  to  [ERANGE].  If  the  integer expression
       (math_errhandling & MATH_ERREXCEPT) is non-zero,  then  the  divide-by-
       zero floating-point exception shall be raised.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       On   error,   the   expressions  (math_errhandling  &  MATH_ERRNO)  and
       (math_errhandling & MATH_ERREXCEPT) are independent of each other,  but
       at least one of them must be non-zero.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       feclearexcept()  ,  fetestexcept() , isnan() , log() , pow() , the Base
       Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment  of
       Error Conditions for Mathematical Functions, <math.h>

COPYRIGHT

       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.opengroup.org/unix/online.html .