Common mathematical functions| Functions | | Basic operations | | | | Maximum/minimum operations | | | | Exponential functions | | | | Power functions | | | | Trigonometric and hyperbolic functions | | |
| | Nearest integer floating-point | | | | Floating-point manipulation | | | | Narrowing operations | | | | Quantum and quantum exponent | | | | Decimal re-encoding functions | | | | Total order and payload functions | | | | Classification | | |
| | Error and gamma functions | | | | Types | | | | Macro constants | | Special floating-point values | | | | Arguments and return values | | (C99)(C99)(C99)(C99)(C99) |
| | (C23)(C23)(C23)(C23)(C23) |
| | Error handling | | | | Fast operation indicators | | |
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float atanf(float arg); | (1) | (since C99) |
double atan(double arg); | (2) | |
longdouble atanl(longdouble 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) |
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#define atan( arg ) | (7) | (since C99) |
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1-6) Computes the principal value of the arc tangent ofarg.
7) Type-generic macro: If the argument has type
longdouble,
(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 inmath_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.
POSIX specifies that in case of underflow,arg is returned unmodified, and if that is not supported, an implementation-defined value no greater thanDBL_MIN,FLT_MIN, andLDBL_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 valuesprintf("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)=3.141593atan(Inf) = 1.570796, 2*atan(Inf) = 3.141593atan(-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
| computes arc tangent, using signs to determine quadrants
(function)[edit] |
| computes arc sine (\({\small\arcsin{x} }\)arcsin(x))
(function)[edit] |
| computes arc cosine (\({\small\arccos{x} }\)arccos(x))
(function)[edit] |
| computes tangent (\({\small\tan{x} }\)tan(x))
(function)[edit] |
| computes the complex arc tangent
(function)[edit] |
|
