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
13 atan, atanf, atanl — arc tangent function
14
16 #include <math.h>
17 double atan(double x);
19 float atanf(float x);
20 long double atanl(long double x);
21
23 The functionality described on this reference page is aligned with the
24 ISO C standard. Any conflict between the requirements described here
25 and the ISO C standard is unintentional. This volume of POSIX.1‐2008
26 defers to the ISO C standard.
27 These functions shall compute the principal value of the arc tangent of
29 their argument x.
30 An application wishing to check for error situations should set errno
32 to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
33 functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
34 FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
35 occurred.
36
38 Upon successful completion, these functions shall return the arc tan‐
39 gent of x in the range [−π/2,π/2] radians.
40 If x is NaN, a NaN shall be returned.
42 If x is ±0, x shall be returned.
44 If x is ±Inf, ±π/2 shall be returned.
46 If x is subnormal, a range error may occur
48 and x should be returned.
49 If x is not returned, atan(), atanf(), and atanl() shall return an
51 implementation-defined value no greater in magnitude than DBL_MIN,
52 FLT_MIN, and LDBL_MIN, respectively.
53
55 These functions may fail if:
56 Range Error The value of x is subnormal.
58 If the integer expression (math_errhandling & MATH_ERRNO)
60 is non-zero, then errno shall be set to [ERANGE]. If the
61 integer expression (math_errhandling & MATH_ERREXCEPT) is
62 non-zero, then the underflow floating-point exception shall
63 be raised.
64 The following sections are informative.
66
68 None.
69
71 On error, the expressions (math_errhandling & MATH_ERRNO) and
72 (math_errhandling & MATH_ERREXCEPT) are independent of each other, but
73 at least one of them must be non-zero.
74
76 None.
77
79 None.
80
82 atan2(), feclearexcept(), fetestexcept(), isnan(), tan()
83 The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment of
85 Error Conditions for Mathematical Functions, <math.h>
86
88 Portions of this text are reprinted and reproduced in electronic form
89 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
90 -- Portable Operating System Interface (POSIX), The Open Group Base
91 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
92 cal and Electronics Engineers, Inc and The Open Group. (This is
93 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
94 event of any discrepancy between this version and the original IEEE and
95 The Open Group Standard, the original IEEE and The Open Group Standard
96 is the referee document. The original Standard can be obtained online
97 at http://www.unix.org/online.html .
98 Any typographical or formatting errors that appear in this page are
100 most likely to have been introduced during the conversion of the source
101 files to man page format. To report such errors, see https://www.ker‐
102 nel.org/doc/man-pages/reporting_bugs.html .
103IEEE/The Open Group 2013 ATAN(3P)