1ATAN(3P) POSIX Programmer's Manual ATAN(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 atan, atanf, atanl — arc tangent function
13
15 #include <math.h>
16 double atan(double x);
18 float atanf(float x);
19 long double atanl(long double x);
20
22 The functionality described on this reference page is aligned with the
23 ISO C standard. Any conflict between the requirements described here
24 and the ISO C standard is unintentional. This volume of POSIX.1‐2017
25 defers to the ISO C standard.
26 These functions shall compute the principal value of the arc tangent of
28 their argument x.
29 An application wishing to check for error situations should set errno
31 to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
32 functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
33 FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
34 occurred.
35
37 Upon successful completion, these functions shall return the arc tan‐
38 gent of x in the range [-π/2,π/2] radians.
39 If x is NaN, a NaN shall be returned.
41 If x is ±0, x shall be returned.
43 If x is ±Inf, ±π/2 shall be returned.
45 If x is subnormal, a range error may occur
47 and x should be returned.
48 If x is not returned, atan(), atanf(), and atanl() shall return an
50 implementation-defined value no greater in magnitude than DBL_MIN,
51 FLT_MIN, and LDBL_MIN, respectively.
52
54 These functions may fail if:
55 Range Error The value of x is subnormal.
57 If the integer expression (math_errhandling & MATH_ERRNO)
59 is non-zero, then errno shall be set to [ERANGE]. If the
60 integer expression (math_errhandling & MATH_ERREXCEPT) is
61 non-zero, then the underflow floating-point exception shall
62 be raised.
63 The following sections are informative.
65
67 None.
68
70 On error, the expressions (math_errhandling & MATH_ERRNO) and
71 (math_errhandling & MATH_ERREXCEPT) are independent of each other, but
72 at least one of them must be non-zero.
73
75 None.
76
78 None.
79
81 atan2(), feclearexcept(), fetestexcept(), isnan(), tan()
82 The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of
84 Error Conditions for Mathematical Functions, <math.h>
85
87 Portions of this text are reprinted and reproduced in electronic form
88 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
89 table Operating System Interface (POSIX), The Open Group Base Specifi‐
90 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
91 Electrical and Electronics Engineers, Inc and The Open Group. In the
92 event of any discrepancy between this version and the original IEEE and
93 The Open Group Standard, the original IEEE and The Open Group Standard
94 is the referee document. The original Standard can be obtained online
95 at http://www.opengroup.org/unix/online.html .
96 Any typographical or formatting errors that appear in this page are
98 most likely to have been introduced during the conversion of the source
99 files to man page format. To report such errors, see https://www.ker‐
100 nel.org/doc/man-pages/reporting_bugs.html .
101IEEE/The Open Group 2017 ATAN(3P)