#include <math.h>

double atan(double x);

float atanf(float x);

long double atanl(long double x);


Partially implemented


IEEE Std 1003.1-2017


These functions shall compute the principal value of the arc tangent of their argument 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 arc tangent of x in the range [-PI/2,PI/2] radians.

  • If x is NaN, a NaN shall be returned.

  • If x is ±0, x shall be returned.

  • If x is ±Inf, ±/2 shall be returned.

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

  • If x is not returned, atan(), atanf(), and atanl() shall return an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.


These functions may fail if:

  • Range Error

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.



Known bugs


See Also

  1. Standard library functions
  2. Table of Contents