PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       tan, tanf, tanl — tangent function

SYNOPSIS

       #include <math.h>

       double tan(double x);
       float tanf(float x);
       long double tanl(long double x);

DESCRIPTION

       The  functionality  described  on  this  reference  page is aligned with the ISO C standard. Any conflict
       between the requirements described  here  and  the  ISO C  standard  is  unintentional.  This  volume  of
       POSIX.1‐2008 defers to the ISO C standard.

       These functions shall compute the tangent of their argument x, measured in radians.

       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 tangent of x.

       If the correct value would cause underflow, and is not representable, a range error may occur, and tan(),
       tanf(), and tanl() shall return 0.0, or (if IEC 60559 Floating-Point is not supported) an implementation-
       defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

       If x is NaN, a NaN shall be returned.

       If x is ±0, x shall be returned.

       If x is subnormal, a range error may occur
       and x should be returned.

       If  x  is not returned, tan(), tanf(), and tanl() shall return an implementation-defined value no greater
       in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

       If x is ±Inf, a domain error shall occur, and either a NaN (if supported), or  an  implementation-defined
       value shall be returned.

       If the correct value would cause underflow, and is representable, a range error may occur and the correct
       value shall be returned.

       If the correct value would cause overflow, a range error shall occur and tan(), tanf(), and tanl()  shall
       return  ±HUGE_VAL,  ±HUGE_VALF,  and ±HUGE_VALL, respectively, with the same sign as the correct value of
       the function.

ERRORS

       These functions shall fail if:

       Domain Error
                   The value of 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.

       Range Error The result overflows

                   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 overflow floating-point exception shall be raised.

       These functions may fail if:

       Range Error The result underflows, or the value of x is subnormal.

                   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 underflow floating-point exception shall be raised.

       The following sections are informative.

EXAMPLES

   Taking the Tangent of a 45-Degree Angle
           #include <math.h>
           ...
           double radians = 45.0 * M_PI / 180;
           double result;
           ...
           result = tan (radians);

APPLICATION USAGE

       There are no known floating-point representations such that for  a  normal  argument,  tan(x)  is  either
       overflow or underflow.

       These functions may lose accuracy when their argument is near a multiple of π/2 or is far from 0.0.

       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

       atan(), feclearexcept(), fetestexcept(), isnan()

       The Base Definitions volume of POSIX.1‐2008, Section 4.19, 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, 2013 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications  Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .