std::atan, std::atanf, std::atanl

Defined in header <cmath>
float       atan ( float arg );
float       atanf( float arg );
(since C++11)
double      atan ( double arg );
long double atan ( long double arg );
long double atanl( long double arg );
(since C++11)
double      atan ( IntegralType arg );
(4) (since C++11)
1-3) Computes the principal value of the arc tangent of arg
4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to 2) (the argument is cast to double).


arg - value of a floating-point or Integral type

Return value

If no errors occur, the arc tangent of arg (arctan(arg)) in the range [- π/2 , +π/2] radians, is returned.

If a range error occurs due to underflow, the correct result (after rounding) is returned.

Error handling

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

  • If the argument is ±0, it is returned unmodified
  • If the argument is +∞, +π/2 is returned
  • If the argument is -∞, -π/2 is returned
  • if the argument is NaN, NaN is returned


POSIX specifies that in case of underflow, arg is returned unmodified, and if that is not supported, an implementation-defined value no greater than DBL_MIN, FLT_MIN, and LDBL_MIN is returned.


#include <iostream>
#include <cmath>
int main()
    std::cout << "atan(1) = " << atan(1) << " 4*atan(1) = " << 4*atan(1) << '\n';
    // special values
    std::cout << "atan(Inf) = " << atan(INFINITY)
              << " 2*atan(Inf) = " << 2*atan(INFINITY) << '\n'
              << "atan(-0.0) = " << atan(-0.0) << '\n'
              << "atan(+0.0) = " << atan(0) << '\n';


atan(1) = 0.785398 4*atan(1) = 3.14159
atan(Inf) = 1.5708 2*atan(Inf) = 3.14159
atan(-0.0) = -0
atan(+0.0) = 0

See also

computes arc sine (\({\small\arcsin{x} }\)arcsin(x))
computes arc cosine (\({\small\arccos{x} }\)arccos(x))
arc tangent, using signs to determine quadrants
computes tangent (\({\small\tan{x} }\)tan(x))
computes arc tangent of a complex number (\({\small\arctan{z} }\)arctan(z))
(function template)
applies the function std::atan to each element of valarray
(function template)
C documentation for atan

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