Provided by: manpages-posix-dev_2.16-1_all 
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 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
either 0.0 (if supported), or an implementation-defined 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 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 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 non-zero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
atan() , feclearexcept() , fetestexcept() , isnan() , 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 .