Atan

Defined in header <cmath>.

Description

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 num  (since C++23).
Additional Overloads are provided for all integer types, which are treated as double (since C++11).

Declarations

C++23

// 1)
/* floating-point-type */ atan( /* floating-point-type */ num );
// 2)
float atanf( float num );
// 3)
long double atanl( long double num );

Additional Overloads

// 4)
template< class Integer >
double atan ( Integer num );

C++11

// 1)
float atan ( float num );
// 2)
double atan ( double num );
// 3)
long double atan ( long double num );
// 4)
float atanf( float num );
// 5)
long double atanl( long double num );

Additional Overloads

// 6)
template< class Integer >
double atan ( Integer num );

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 Additional Overloads. 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)).

Examples

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

Result

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