
TAN(3P) POSIX Programmer's Manual TAN(3P)
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
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 nonzero,
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 either 0.0 (if supported), or an implementationdefined value shall be
returned.
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 +Inf, a domain error shall occur, and either a NaN (if supported), or an imple
mentationdefined 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 nonzero, then errno shall be
set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is nonzero,
then the invalid floatingpoint exception shall be raised.
Range Error
The result overflows
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the overflow floatingpoint 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 nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the underflow floatingpoint exception shall be raised.
The following sections are informative.
EXAMPLES
Taking the Tangent of a 45Degree Angle
#include <math.h>
...
double radians = 45.0 * M_PI / 180;
double result;
...
result = tan (radians);
APPLICATION USAGE
There are no known floatingpoint 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 pi/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 nonzero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
atan(), feclearexcept(), fetestexcept(), isnan(), the Base Definitions volume of
IEEE Std 1003.12001, Section 4.18, Treatment of Error Conditions for Mathematical Func
tions, <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) 20012003 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 orig
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 TAN(3P) 
