1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
|
<h1 id="firstHeading" class="firstHeading">acos, acosf, acosl</h1> <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code><math.h></code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">float acosf( float arg );</pre>
</td> <td> (1) </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> <tr class="t-dcl"> <td> <pre data-language="c">double acos( double arg );</pre>
</td> <td> (2) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">long double acosl( long double arg );</pre>
</td> <td> (3) </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> <tr class="t-dcl t-since-c23"> <td> <pre data-language="c">_Decimal32 acosd32( _Decimal32 arg );</pre>
</td> <td> (4) </td> <td> <span class="t-mark-rev t-since-c23">(since C23)</span> </td> </tr> <tr class="t-dcl t-since-c23"> <td> <pre data-language="c">_Decimal64 acosd64( _Decimal64 arg );</pre>
</td> <td> (5) </td> <td> <span class="t-mark-rev t-since-c23">(since C23)</span> </td> </tr> <tr class="t-dcl t-since-c23"> <td> <pre data-language="c">_Decimal128 acosd128( _Decimal128 arg );</pre>
</td> <td> (6) </td> <td> <span class="t-mark-rev t-since-c23">(since C23)</span> </td> </tr> <tr class="t-dsc-header"> <th> Defined in header <code><tgmath.h></code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">#define acos( arg )</pre>
</td> <td> (7) </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> </table> <div class="t-li1">
<span class="t-li">1-6)</span> Computes the principal value of the arc cosine of <code>arg</code>.</div> <div class="t-li1">
<span class="t-li">7)</span> Type-generic macro: If the argument has type <code>long double</code>, <span class="t-v">(3)</span> (<code>acosl</code>) is called. Otherwise, if the argument has integer type or the type <code>double</code>, <span class="t-v">(2)</span> (<code>acos</code>) is called. Otherwise, <span class="t-v">(1)</span> (<code>acosf</code>) is called. If the argument is complex, then the macro invokes the corresponding complex function (<code><a href="../complex/cacos" title="c/numeric/complex/cacos">cacosf</a></code>, <code><a href="../complex/cacos" title="c/numeric/complex/cacos">cacos</a></code>, <code><a href="../complex/cacos" title="c/numeric/complex/cacos">cacosl</a></code>).</div> <table class="t-rev-begin"> <tr class="t-rev t-since-c23">
<td> <p>The functions <span class="t-v">(4-6)</span> are declared if and only if the implementation predefines <code>__STDC_IEC_60559_DFP__</code> (i.e. the implementation supports decimal floating-point numbers).</p>
</td> <td><span class="t-mark-rev t-since-c23">(since C23)</span></td>
</tr> </table> <h3 id="Parameters"> Parameters</h3> <table class="t-par-begin"> <tr class="t-par"> <td> arg </td> <td> - </td> <td> floating-point value </td>
</tr>
</table> <h3 id="Return_value"> Return value</h3> <p>If no errors occur, the arc cosine of <code>arg</code> (arccos(arg)) in the range [0 ; π], is returned.</p>
<p>If a domain error occurs, an implementation-defined value is returned (NaN where supported).</p>
<p>If a range error occurs due to underflow, the correct result (after rounding) is returned.</p>
<h3 id="Error_handling"> Error handling</h3> <p>Errors are reported as specified in <a href="math_errhandling" title="c/numeric/math/math errhandling"><code>math_errhandling</code></a>.</p>
<p>Domain error occurs if <code>arg</code> is outside the range <code>[-1.0; 1.0]</code>.</p>
<p>If the implementation supports IEEE floating-point arithmetic (IEC 60559):</p>
<ul>
<li> If the argument is +1, the value <code>+0</code> is returned; </li>
<li> If |arg| > 1, a domain error occurs and NaN is returned; </li>
<li> if the argument is NaN, NaN is returned. </li>
</ul> <h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#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 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");
}</pre></div> <p>Possible output:</p>
<div class="text source-text"><pre data-language="c">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</pre></div> </div> <h3 id="References"> References</h3> <ul>
<li> C23 standard (ISO/IEC 9899:2023): </li>
<ul>
<li> 7.12.4.1 The acos functions (p: TBD) </li>
<li> 7.25 Type-generic math <tgmath.h> (p: TBD) </li>
<li> F.10.1.1 The acos functions (p: TBD) </li>
</ul>
<li> C17 standard (ISO/IEC 9899:2018): </li>
<ul>
<li> 7.12.4.1 The acos functions (p: 173) </li>
<li> 7.25 Type-generic math <tgmath.h> (p: 272-273) </li>
<li> F.10.1.1 The acos functions (p: 378) </li>
</ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul>
<li> 7.12.4.1 The acos functions (p: 238) </li>
<li> 7.25 Type-generic math <tgmath.h> (p: 373-375) </li>
<li> F.10.1.1 The acos functions (p: 518) </li>
</ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul>
<li> 7.12.4.1 The acos functions (p: 218) </li>
<li> 7.22 Type-generic math <tgmath.h> (p: 335-337) </li>
<li> F.9.1.1 The acos functions (p: 455) </li>
</ul>
<li> C89/C90 standard (ISO/IEC 9899:1990): </li>
<ul><li> 4.5.2.1 The acos function </li></ul>
</ul> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="asin" title="c/numeric/math/asin"> <span class="t-lines"><span>asin</span><span>asinf</span><span>asinl</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> computes arc sine (\({\small\arcsin{x} }\)arcsin(x)) <br> <span class="t-mark">(function)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="atan" title="c/numeric/math/atan"> <span class="t-lines"><span>atan</span><span>atanf</span><span>atanl</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> computes arc tangent (\({\small\arctan{x} }\)arctan(x)) <br> <span class="t-mark">(function)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="atan2" title="c/numeric/math/atan2"> <span class="t-lines"><span>atan2</span><span>atan2f</span><span>atan2l</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> computes arc tangent, using signs to determine quadrants <br> <span class="t-mark">(function)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="cos" title="c/numeric/math/cos"> <span class="t-lines"><span>cos</span><span>cosf</span><span>cosl</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> computes cosine (\({\small\cos{x} }\)cos(x)) <br> <span class="t-mark">(function)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="../complex/cacos" title="c/numeric/complex/cacos"> <span class="t-lines"><span>cacos</span><span>cacosf</span><span>cacosl</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> computes the complex arc cosine <br> <span class="t-mark">(function)</span> </td>
</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/numeric/math/acos" title="cpp/numeric/math/acos">C++ documentation</a></span> for <code>acos</code> </td>
</tr> </table> <div class="_attribution">
<p class="_attribution-p">
© cppreference.com<br>Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.<br>
<a href="https://en.cppreference.com/w/c/numeric/math/acos" class="_attribution-link">https://en.cppreference.com/w/c/numeric/math/acos</a>
</p>
</div>
|
