acos, acosf, acosl

 

C

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headers

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Dynamic memory management

Error handling

Program utilities

Variadic function support

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

Technical Specifications

 

Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

Random number generation

Type-generic math

 

Common mathematical functions

Functions
Basic operations
abslabsllabsimaxabs (C99) fabs divldivlldivimaxdiv (C99) fmod	remainder (C99) remquo (C99) fma (C99) fmax (C99) fmin (C99) fdim (C99) nannanfnanl (C99)(C99)(C99)
Exponential functions
exp exp2 (C99) expm1 (C99)	log log10 log1p (C99) log2 (C99)
Power functions
sqrt cbrt (C99)	hypot (C99) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	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)	trunc (C99) nearbyint (C99) rintlrintllrint (C99)(C99)(C99)
Floating point manipulation functions
ldexp scalbnscalbln (C99)(C99) ilogb (C99) logb (C99)	frexp modf nextafternexttoward (C99)(C99) copysign (C99)
Classification
fpclassify (C99) isfinite (C99) isinf (C99) isnan (C99) isnormal (C99) signbit (C99)	isgreater (C99) isgreaterequal (C99) isless (C99) islessequal (C99) islessgreater (C99) isunordered (C99)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C99)(C99)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)

 

Defined in header <math.h>
float       acosf( float arg );	(1)	(since C99)
double      acos( double arg );	(2)
long double acosl( long double arg );	(3)	(since C99)
Defined in header <tgmath.h>
#define acos( arg )	(4)	(since C99)

1-3) Computes the principal value of the arc cosine of arg.

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

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 <stdio.h>
#include <math.h>
#include <errno.h>
#include <fenv.h>
#include <string.h>
 
#pragma STDC FENV_ACCESS ON
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 handling 
    errno = 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

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