atan, atanf, atanl - cppreference.com (original) (raw)

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

1. 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).

Contents

• 1 Parameters
• 2 Return value
• 3 Error handling
• 4 Notes
• 5 Example
• 6 References
• 7 See also

[edit] Parameters

[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 ±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.

[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, 4atan(1)=%f\n", atan(1), 4 * atan(1)); // special values printf("atan(Inf) = %f, 2atan(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, 4atan(1)=3.141593 atan(Inf) = 1.570796, 2atan(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