acos, acosf, acosl

 

C

Compiler support

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

 

Numerics

Common mathematical functions

Floating-point environment(C99)

Pseudo-random number generation

Complex number arithmetic(C99)

Type-generic math(C99)

Bit manipulation(C23)

Checked integer arithmetic(C23)

 

Common mathematical functions

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) fmin (C99) fmaximum (C23) fminimum (C23) fmaximum_mag (C23)  fmaximum_num (C23) fminimum_mag (C23) fminimum_num (C23) fmaximum_mag_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)

Nearest integer floating-point ceil floor roundlroundllround (C99)(C99)(C99) roundeven (C23) trunc (C99) nearbyint (C99) rintlrintllrint (C99)(C99)(C99) fromfpfromfpxufromfpufromfpx (C23)(C23)(C23)(C23) Floating-point manipulation 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 quantizedN (C23) quantumdN (C23) samequantumdN (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)

Error and gamma functions erf (C99) erfc (C99) lgamma (C99) tgamma (C99) 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_VALHUGE_VALFHUGE_VALLHUGE_VALDN (C99)(C99)(C23) INFINITYDEC_INFINITY (C99)(C23) NANDEC_NAN (C99)(C23) Arguments and return values FP_ILOGB0FP_ILOGBNAN (C99)(C99) FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99) FP_LLOGB0FP_LLOGBNAN (C23)(C23) FP_INT_UPWARDFP_INT_DOWNWARDFP_INT_TOWARDZEROFP_INT_TONEARESTFROMZEROFP_INT_TONEAREST (C23)(C23)(C23)(C23)(C23) Error handling MATH_ERRNOMATH_ERRNOEXCEPT (C99)(C99)  math_errhandling (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       acosf(float arg );	(1)	(since C99)
double      acos(double arg );	(2)
longdouble acosl(longdouble arg );	(3)	(since C99)
_Decimal32  acosd32( _Decimal32 arg );	(4)	(since C23)
_Decimal64  acosd64( _Decimal64 arg );	(5)	(since C23)
_Decimal128 acosd128( _Decimal128 arg );	(6)	(since C23)
Defined in header <tgmath.h>
#define acos( arg )	(7)	(since C99)

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

7) Type-generic macro: If the argument has type longdouble, (3) (acosl) is called. Otherwise, if the argument has integer type or the type double, (2) (acos) is called. Otherwise, (1) (acosf) is called. If the argument is complex, then the macro invokes the corresponding complex function (cacosf, cacos, cacosl).

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 cosine of arg (arccos(arg)) in the range [0 ; π], is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

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.

Domain error occurs if arg is outside the range [-1.0; 1.0].

If the implementation supports IEEE floating-point arithmetic (IEC 60559):

• If the argument is +1, the value +0 is returned;
• If |arg| > 1, a domain error occurs and NaN is returned;
• if the argument is NaN, NaN is returned.

Example

Run this code

#include <errno.h>#include <fenv.h>#include <math.h>#include <stdio.h>#include <string.h>   #ifndef __GNUC__#pragma STDC FENV_ACCESS ON#endif   int main(void){printf("acos(-1) = %f\n", acos(-1));printf("acos(0.0) = %f 2*acos(0.0) = %f\n", acos(0), 2* acos(0));printf("acos(0.5) = %f 3*acos(0.5) = %f\n", acos(0.5), 3* acos(0.5));printf("acos(1) = %f\n", acos(1));   // error handlingerrno=0;feclearexcept(FE_ALL_EXCEPT);printf("acos(1.1) = %f\n", acos(1.1));if(errno==EDOM)perror(" errno == EDOM");if(fetestexcept(FE_INVALID))puts(" FE_INVALID raised");}

Possible output:

acos(-1) = 3.141593 acos(0.0) = 1.570796 2*acos(0.0) = 3.141593 acos(0.5) = 1.047198 3*acos(0.5) = 3.141593 acos(1) = 0.000000 acos(1.1) = nan errno == EDOM: Numerical argument out of domain FE_INVALID raised

References

• C23 standard (ISO/IEC 9899:2024):

• 7.12.4.1 The acos functions (p: TBD)

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

• F.10.1.1 The acos functions (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• 7.12.4.1 The acos functions (p: 173)

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

• F.10.1.1 The acos functions (p: 378)

• C11 standard (ISO/IEC 9899:2011):

• 7.12.4.1 The acos functions (p: 238)

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

• F.10.1.1 The acos functions (p: 518)

• C99 standard (ISO/IEC 9899:1999):

• 7.12.4.1 The acos functions (p: 218)

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

• F.9.1.1 The acos functions (p: 455)

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

• 4.5.2.1 The acos function

See also

asinasinfasinl (C99)(C99)	computes arc sine (\({\small\arcsin{x} }\)arcsin(x)) (function)
atanatanfatanl (C99)(C99)	computes arc tangent (\({\small\arctan{x} }\)arctan(x)) (function)
atan2atan2fatan2l (C99)(C99)	computes arc tangent, using signs to determine quadrants (function)
coscosfcosl (C99)(C99)	computes cosine (\({\small\cos{x} }\)cos(x)) (function)
cacoscacosfcacosl (C99)(C99)(C99)	computes the complex arc cosine (function)
C++ documentation for acos