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Showing content from https://en.cppreference.com/w/cpp/algorithm/../algorithm/../../cpp/../c/numeric/math/atan.html below:

atan, atanf, atanl - cppreference.com

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)

#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) [edit] Parameters arg - floating-point value [edit] Return value

If no errors occur, the arc tangent of

arg

(

arctan(arg)

) in the range

[- ; +]

radians, is returned.

If a range error occurs due to underflow, the correct result (after rounding) is returned.

[edit] Error handling

Errors are reported as specified in math_errhandling.

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

if the argument is Â±0, it is returned unmodified;
if the argument is +â, +π/2 is returned;
if the argument is -â, -π/2 is returned;
if the argument is NaN, NaN is returned.

[edit] 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.

[edit] Example

#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

[edit] References

C23 standard (ISO/IEC 9899:2024):

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

[edit] See also

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