atan, atanf, atanl

Functions

Basic operations

abslabsllabsimaxabs (C99)(C99)
fabs
divldivlldivimaxdiv (C99)(C99)

fmod
remainder (C99)
remquo (C99)
fma (C99)
fdim (C99)
nannanfnanlnandN (C99)(C99)(C99)(C23)

Maximum/minimum operations

fmax (C99)
fmaximum (C23)
fmaximum_mag (C23)
fmaximum_num (C23)
fmaximum_mag_num (C23)

fmin (C99)
fminimum (C23)
fminimum_mag (C23)
fminimum_num (C23)
fminimum_mag_num (C23)

Exponential functions

exp
exp10 (C23)
exp2 (C99)
expm1 (C99)
exp10m1 (C23)
exp2m1 (C23)

log
log10
log2 (C99)
log1plogp1 (C99)(C23)
log10p1 (C23)
log2p1 (C23)

Power functions

sqrt
cbrt (C99)
rootn (C23)
rsqrt (C23)

hypot (C99)
compound (C23)
pow
pown (C23)
powr (C23)

Trigonometric and hyperbolic functions

sin
cos
tan
asin
acos
atan
atan2
sinpi (C23)
cospi (C23)
tanpi (C23)

asinpi (C23)
acospi (C23)
atanpi (C23)
atan2pi (C23)
sinh
cosh
tanh
asinh (C99)
acosh (C99)
atanh (C99)

Error and gamma functions

erf (C99)
erfc (C99)

lgamma (C99)
tgamma (C99)

Nearest integer floating-point operations

ceil
floor
roundlroundllround (C99)(C99)(C99)
roundeven (C23)
trunc (C99)

nearbyint (C99)
rintlrintllrint (C99)(C99)(C99)
fromfpfromfpxufromfpufromfpx (C23)(C23)(C23)(C23)

Floating-point manipulation functions

ldexp
frexp
scalbnscalbln (C99)(C99)
ilogbllogb (C99)(C23)
logb (C99)

modf
nextafternexttoward (C99)(C99)
nextupnextdown (C23)(C23)
copysign (C99)
canonicalize (C23)

Narrowing operations

fadd (C23)
fsub (C23)
fmul (C23)

fdiv (C23)
ffma (C23)
fsqrt (C23)

Quantum and quantum exponent functions

quantizedN (C23)
samequantumdN (C23)

quantumdN (C23)
llquantexpdN (C23)

Decimal re-encoding functions

encodedecdN (C23)
decodedecdN (C23)

encodebindN (C23)
decodebindN (C23)

Total order and payload functions

totalorder (C23)
getpayload (C23)

setpayload (C23)
setpayloadsig (C23)

Classification

fpclassify (C99)
iscanonical (C23)
isfinite (C99)
isinf (C99)
isnan (C99)
isnormal (C99)
signbit (C99)
issubnormal (C23)
iszero (C23)

isgreater (C99)
isgreaterequal (C99)
isless (C99)
islessequal (C99)
islessgreater (C99)
isunordered (C99)
issignaling (C23)
iseqsig (C23)

Types

div_tldiv_tlldiv_timaxdiv_t (C99)(C99)

float_tdouble_t (C99)(C99)
_Decimal32_t_Decimal64_t (C23)(C23)

Macro constants

Special floating-point values

HUGE_VALFHUGE_VALHUGE_VALLHUGE_VALDN

(C99)(C99)(C23)

INFINITYDEC_INFINITY (C99)(C23)
NANDEC_NAN (C99)(C23)

Arguments and return values

FP_ILOGB0FP_ILOGBNAN (C99)(C99)
FP_INT_UPWARDFP_INT_DOWNWARDFP_INT_TOWARDZEROFP_INT_TONEARESTFROMZEROFP_INT_TONEAREST (C23)(C23)(C23)(C23)(C23)

FP_LLOGB0FP_LLOGBNAN (C23)(C23)
FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)

Error handling

math_errhandlingMATH_ERRNOMATH_ERRNOEXCEPT

(C99)(C99)(C99)

Fast operation indicators

FP_FAST_FMAFFP_FAST_FMA (C99)(C99)
FP_FAST_FADDFP_FAST_FADDLFP_FAST_DADDLFP_FAST_DMADDDN (C23)(C23)(C23)(C23)
FP_FAST_FMULFP_FAST_FMULLFP_FAST_DMULLFP_FAST_DMMULDN (C23)(C23)(C23)(C23)
FP_FAST_FFMAFP_FAST_FFMALFP_FAST_DFMALFP_FAST_DMFMADN (C23)(C23)(C23)(C23)

FP_FAST_FMALFP_FAST_FMADN (C99)(C23)
FP_FAST_FSUBFP_FAST_FSUBLFP_FAST_DSUBLFP_FAST_DMSUBDN (C23)(C23)(C23)(C23)
FP_FAST_FDIVFP_FAST_FDIVLFP_FAST_DDIVLFP_FAST_DMDIVDN (C23)(C23)(C23)(C23)
FP_FAST_FSQRTFP_FAST_FSQRTLFP_FAST_DSQRTLFP_FAST_DMSQRTDN (C23)(C23)(C23)(C23)

Defined in header `<math.h>`
float atanf( float arg );	(1)	(since C99)
double atan( double arg );	(2)
long double atanl( long double arg );	(3)	(since C99)
_Decimal32 atand32( _Decimal32 arg );	(4)	(since C23)
_Decimal64 atand64( _Decimal64 arg );	(5)	(since C23)
_Decimal128 atand128( _Decimal128 arg );	(6)	(since C23)
Defined in header `<tgmath.h>`
#define atan( arg )	(7)	(since C99)

1-6) Computes the principal value of the arc tangent of arg.

7) Type-generic macro: If the argument has type long double, (3) (atanl) is called. Otherwise, if the argument has integer type or the type double, (2) (atan) is called. Otherwise, (1) (atanf) is called. If the argument is complex, then the macro invokes the corresponding complex function (catanf, catan, catanl).

The functions (4-6) are declared if and only if the implementation predefines __STDC_IEC_60559_DFP__ (i.e. the implementation supports decimal floating-point numbers).

(since C23)

Parameters

arg

-

floating point value

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.

Notes

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.

Example

Run this code

#include <math.h>
#include <stdio.h>
 
int main(void)
{
    printf("atan(1) = %f, 4*atan(1)=%f\n", atan(1), 4 * atan(1));
    // special values
    printf("atan(Inf) = %f, 2*atan(Inf) = %f\n", atan(INFINITY), 2 * atan(INFINITY));
    printf("atan(-0.0) = %+f, atan(+0.0) = %+f\n", atan(-0.0), atan(0));
}

Output:

atan(1) = 0.785398, 4*atan(1)=3.141593
atan(Inf) = 1.570796, 2*atan(Inf) = 3.141593
atan(-0.0) = -0.000000, atan(+0.0) = +0.000000

References

C23 standard (ISO/IEC 9899:2023):

7.12.4.3 The atan functions (p: TBD)

7.25 Type-generic math <tgmath.h> (p: TBD)

F.10.1.3 The atan functions (p: TBD)

C17 standard (ISO/IEC 9899:2018):

7.12.4.3 The atan functions (p: 174)

7.25 Type-generic math <tgmath.h> (p: 272-273)

F.10.1.3 The atan functions (p: 378)

C11 standard (ISO/IEC 9899:2011):

7.12.4.3 The atan functions (p: 238-239)

7.25 Type-generic math <tgmath.h> (p: 373-375)

F.10.1.3 The atan functions (p: 519)

C99 standard (ISO/IEC 9899:1999):

7.12.4.3 The atan functions (p: 219)

7.22 Type-generic math <tgmath.h> (p: 335-337)

F.9.1.3 The atan functions (p: 456)

C89/C90 standard (ISO/IEC 9899:1990):

4.5.2.3 The atan function

Language
Headers
Type support
Program utilities
Variadic function support
Error handling
Dynamic memory management
Strings library
Algorithms
Numerics
Date and time utilities
Input/output support
Localization support
Concurrency support (C11)
Technical Specifications
Symbol index

Common mathematical functions
Floating-point environment (C99)
Pseudo-random number generation
Complex number arithmetic (C99)
Type-generic math (C99)

atan2atan2fatan2l (C99)(C99)	computes arc tangent, using signs to determine quadrants (function)
asinasinfasinl (C99)(C99)	computes arc sine (\({\small\arcsin{x} }\) $arcsin(x)$ ) (function)
acosacosfacosl (C99)(C99)	computes arc cosine (\({\small\arccos{x} }\) $arccos(x)$ ) (function)
tantanftanl (C99)(C99)	computes tangent (\({\small\tan{x} }\) $tan(x)$ ) (function)
catancatanfcatanl (C99)(C99)(C99)	computes the complex arc tangent (function)

atan, atanf, atanl

Parameters

Return value

Error handling

Notes

Example

References

See also

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