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

(哋它亢++17)

lcm

(哋它亢++17)

Interpolations

midpoint

(哋它亢++20)

lerp

(哋它亢++20)

Saturation arithmetic

add_sat (哋它亢++26)
sub_sat (哋它亢++26)
saturate_cast (哋它亢++26)

mul_sat (哋它亢++26)
div_sat (哋它亢++26)

Generic numeric operations

iota (哋它亢++11)
ranges::iota (哋它亢++23)
accumulate
inner_product
adjacent_difference
partial_sum

reduce (哋它亢++17)
transform_reduce (哋它亢++17)
inclusive_scan (哋它亢++17)
exclusive_scan (哋它亢++17)
transform_inclusive_scan (哋它亢++17)
transform_exclusive_scan (哋它亢++17)

Bit operations

has_single_bit (哋它亢++20)
bit_cast (哋它亢++20)
bit_ceil (哋它亢++20)
bit_floor (哋它亢++20)
bit_width (哋它亢++20)
rotl (哋它亢++20)
rotr (哋它亢++20)

popcount (哋它亢++20)
countl_zero (哋它亢++20)
countl_one (哋它亢++20)
countr_zero (哋它亢++20)
countr_one (哋它亢++20)
byteswap (哋它亢++23)
endian (哋它亢++20)

Common mathematical functions

Functions

Basic operations

abs(int)labsllabsimaxabs (哋它亢++11)
abs(float)fabs
divldivlldivimaxdiv (哋它亢++11)
fmod

remainder (哋它亢++11)
remquo (哋它亢++11)
fma (哋它亢++11)
fmax (哋它亢++11)
fmin (哋它亢++11)
fdim (哋它亢++11)
nannanfnanl (哋它亢++11)(哋它亢++11)(哋它亢++11)

Exponential functions

exp
exp2 (哋它亢++11)
expm1 (哋它亢++11)

log
log10
log1p (哋它亢++11)
log2 (哋它亢++11)

Power functions

sqrt
cbrt (哋它亢++11)

hypot (哋它亢++11)
pow

Trigonometric and hyperbolic functions

sin
cos
tan
asin
acos
atan
atan2

sinh
cosh
tanh
asinh (哋它亢++11)
acosh (哋它亢++11)
atanh (哋它亢++11)

Error and gamma functions

erf (哋它亢++11)
erfc (哋它亢++11)

lgamma (哋它亢++11)
tgamma (哋它亢++11)

Nearest integer floating point operations

ceil
floor
roundlroundllround (哋它亢++11)(哋它亢++11)(哋它亢++11)

trunc (哋它亢++11)
nearbyint (哋它亢++11)
rintlrintllrint (哋它亢++11)(哋它亢++11)(哋它亢++11)

Floating point manipulation functions

ldexp
scalbnscalbln (哋它亢++11)(哋它亢++11)
ilogb (哋它亢++11)
logb (哋它亢++11)

frexp
modf
nextafternexttoward (哋它亢++11)(哋它亢++11)
copysign (哋它亢++11)

Classification/Comparison

fpclassify (哋它亢++11)
isfinite (哋它亢++11)
isinf (哋它亢++11)
isnan (哋它亢++11)
isnormal (哋它亢++11)
signbit (哋它亢++11)

isgreater (哋它亢++11)
isgreaterequal (哋它亢++11)
isless (哋它亢++11)
islessequal (哋它亢++11)
islessgreater (哋它亢++11)
isunordered (哋它亢++11)

Macro constants

HUGE_VALFHUGE_VALHUGE_VALL (哋它亢++11)(哋它亢++11)
INFINITY (哋它亢++11)
NAN (哋它亢++11)
math_errhandlingMATH_ERRNOMATH_ERREXCEPT (哋它亢++11)

FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN

(哋它亢++11)(哋它亢++11)(哋它亢++11)(哋它亢++11)(哋它亢++11)

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

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

(since 哋它亢++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 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

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (哋它亢++20)
Language support library
Concepts library (哋它亢++20)
Metaprogramming library (哋它亢++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (哋它亢++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (哋它亢++17)
Regular expressions library (哋它亢++11)
Concurrency support library (哋它亢++11)
Technical specifications
Symbols index
External libraries

asinasinfasinl (哋它亢++11)(哋它亢++11)	computes arc sine (\({\small\arcsin{x}}\) $arcsin(x)$ ) (function)
acosacosfacosl (哋它亢++11)(哋它亢++11)	computes arc cosine (\({\small\arccos{x}}\) $arccos(x)$ ) (function)
atan2atan2fatan2l (哋它亢++11)(哋它亢++11)	arc tangent, using signs to determine quadrants (function)
tantanftanl (哋它亢++11)(哋它亢++11)	computes tangent (\({\small\tan{x}}\) $tan(x)$ ) (function)
atan(std::complex) (哋它亢++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)