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

abs(int)labsllabsimaxabs (C++11)
abs(float)fabs
divldivlldivimaxdiv (C++11)

fmod
remainder (C++11)
remquo (C++11)
fma (C++11)
fmax (C++11)
fmin (C++11)
fdim (C++11)
nannanfnanl (C++11)(C++11)(C++11)

Exponential functions

exp
exp2 (C++11)
expm1 (C++11)

log
log10
log1p (C++11)
log2 (C++11)

Power functions

sqrt
cbrt (C++11)

hypot (C++11)
pow

Trigonometric and
hyperbolic functions

sin
cos
tan
asin
acos
atan
atan2

sinh
cosh
tanh
asinh (C++11)
acosh (C++11)
atanh (C++11)

Error and gamma functions

erf (C++11)
erfc (C++11)

lgamma (C++11)
tgamma (C++11)

Nearest integer floating point operations

ceil
floor
roundlroundllround (C++11)(C++11)(C++11)

trunc (C++11)
nearbyint (C++11)
rintlrintllrint (C++11)(C++11)(C++11)

Floating point manipulation functions

ldexp
scalbnscalbln (C++11)(C++11)
ilogb (C++11)
logb (C++11)

frexp
modf
nextafternexttoward (C++11)(C++11)
copysign (C++11)

Classification and comparison

fpclassify (C++11)
isfinite (C++11)
isinf (C++11)
isnan (C++11)
isnormal (C++11)
signbit (C++11)

isgreater (C++11)
isgreaterequal (C++11)
isless (C++11)
islessequal (C++11)
islessgreater (C++11)
isunordered (C++11)

Types

div_t
ldiv_t
lldiv_t (C++11)

imaxdiv_t (C++11)
float_t (C++11)
double_t (C++11)

Macro constants

HUGE_VALFHUGE_VALHUGE_VALL (C++11)(C++11)
math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)
INFINITY (C++11)
NAN (C++11)

Classification
FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C++11) (C++11) (C++11) (C++11) (C++11)

Defined in header `<cmath>`
	(1)
float atan ( float num ) ; double atan ( double num ); long double atan ( long double num ) ;			(until C++23)
/floating-point-type/ atan ( /floating-point-type/ num ) ;			(since C++23) (constexpr since C++26)
float atanf( float num );		(2)	(since C++11) (constexpr since C++26)
long double atanl( long double num ) ;		(3)	(since C++11) (constexpr since C++26)
SIMD overload (since C++26)
Defined in header `<simd>`
template < /math-floating-point/ V > constexpr /deduced-simd-t/<V> atan ( const V& v_num ) ;		(S)	(since C++26)
Additional overloads (since C++11)
Defined in header `<cmath>`
template < class Integer > double atan ( Integer num ) ;		(A)	(constexpr since C++26)

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)

S) The SIMD overload performs an element-wise std::atan on v_num.

(See math-floating-point and deduced-simd-t

(since C++26)

A) Additional overloads are provided for all integer types, which are treated as double.

(since C++11)

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

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

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Diagnostics library
Memory management library
Metaprogramming library (C++11)
General utilities library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library (C++17)
Concurrency support library (C++11)
Execution support library (C++26)
Technical specifications
Symbols index
External libraries

asinasinfasinl (C++11)(C++11)	computes arc sine (\({\small\arcsin{x}}\) $arcsin(x)$ ) (function)
acosacosfacosl (C++11)(C++11)	computes arc cosine (\({\small\arccos{x}}\) $arccos(x)$ ) (function)
atan2atan2fatan2l (C++11)(C++11)	arc tangent, using signs to determine quadrants (function)
tantanftanl (C++11)(C++11)	computes tangent (\({\small\tan{x}}\) $tan(x)$ ) (function)
atan(std::complex) (C++11)	computes arc tangent of a complex number (\({\small\arctan{z}}\) $arctan(z)$ ) (function template)
atan(std::valarray)	applies the function std::atan to each element of valarray (function template)
C documentation for atan