NAME¶

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

Synopsis¶

Defined in header <cmath>
float atan ( float num );

double atan ( double num ); (until C++23)

long double atan ( long double num );
/* floating-point-type */ (since C++23)
atan ( /* floating-point-type */ num ); (constexpr since C++26)
float atanf( float num ); (1) (2) (since C++11)
(constexpr since C++26)
long double atanl( long double num ); (3) (since C++11)
(constexpr since C++26)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer > (A) (constexpr since C++26)
double atan ( Integer num );

1-3) Computes the principal value of the arc tangent of num.
The library provides overloads of std::atan for all cv-unqualified floating-point
types as the type of the parameter.
(since C++23)

A) Additional overloads are provided for all integer types, which are (since C++11)
treated as double.

Parameters¶

num - floating-point or integer value

Return value¶

If no errors occur, the arc tangent of num (arctan(num)) 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.

Notes¶

POSIX specifies that in case of underflow, num 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.

The additional overloads are not required to be provided exactly as (A). They only
need to be sufficient to ensure that for their argument num of integer type,
std::atan(num) has the same effect as std::atan(static_cast<double>(num)).

Example¶

// Run this code

#include <cmath>
#include <iostream>

int main()
{
std::cout << "atan(1) = " << std::atan(1) << '\n'
<< "4*atan(1) = " << 4 * std::atan(1) << '\n';

// special values
std::cout << "atan(Inf) = " << std::atan(INFINITY) << '\n'
<< "2*atan(Inf) = " << 2 * std::atan(INFINITY) << '\n'
<< "atan(-0.0) = " << std::atan(-0.0) << '\n'
<< "atan(+0.0) = " << std::atan(0) << '\n';
}

Output:¶

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¶

asin
asinf computes arc sine (\({\small\arcsin{x}}\)arcsin(x))
asinl (function)
(C++11)
(C++11)
acos
acosf computes arc cosine (\({\small\arccos{x}}\)arccos(x))
acosl (function)
(C++11)
(C++11)
atan2
atan2f arc tangent, using signs to determine quadrants
atan2l (function)
(C++11)
(C++11)
tan
tanf computes tangent (\({\small\tan{x}}\)tan(x))
tanl (function)
(C++11)
(C++11)
atan(std::complex) computes arc tangent of a complex number
(C++11) (\({\small\arctan{z}}\)arctan(z))
(function template)
atan(std::valarray) applies the function std::atan to each element of valarray
(function template)
C documentation for
atan