isnan(3)

1FPCLASSIFY(3)              Linux Programmer's Manual             FPCLASSIFY(3)
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NAME

6       fpclassify, isfinite, isnormal, isnan, isinf - floating-point classifi‐
7       cation macros
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SYNOPSIS

10       #include <math.h>
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12       int fpclassify(x);
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14       int isfinite(x);
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16       int isnormal(x);
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18       int isnan(x);
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20       int isinf(x);
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22       Link with -lm.
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24   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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26       fpclassify(), isfinite(), isnormal():
27           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
28       isnan():
29           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
30               || _XOPEN_SOURCE
31               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
32               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
33       isinf():
34           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
35               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
36               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

39       Floating point numbers can have special values,  such  as  infinite  or
40       NaN.   With  the  macro  fpclassify(x) you can find out what type x is.
41       The macro takes any floating-point expression as argument.  The  result
42       is one of the following values:
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44       FP_NAN        x is "Not a Number".
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46       FP_INFINITE   x is either positive infinity or negative infinity.
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48       FP_ZERO       x is zero.
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50       FP_SUBNORMAL  x is too small to be represented in normalized format.
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52       FP_NORMAL     if nothing of the above is correct then it must be a nor‐
53                     mal floating-point number.
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55       The other macros provide a short answer to some standard questions.
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57       isfinite(x)   returns a nonzero value if
58                     (fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)
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60       isnormal(x)   returns a nonzero value if (fpclassify(x) == FP_NORMAL)
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62       isnan(x)      returns a nonzero value if (fpclassify(x) == FP_NAN)
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64       isinf(x)      returns 1 if x is positive infinity, and -1 if x is nega‐
65                     tive infinity.
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ATTRIBUTES

68       For   an   explanation   of   the  terms  used  in  this  section,  see
69       attributes(7).
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71       ┌─────────────────────────────┬───────────────┬─────────┐
72       │Interface                    │ Attribute     │ Value   │
73       ├─────────────────────────────┼───────────────┼─────────┤
74       │fpclassify(), isfinite(),    │ Thread safety │ MT-Safe │
75       │isnormal(), isnan(), isinf() │               │         │
76       └─────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

78       POSIX.1-2001, POSIX.1-2008, C99.
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80       For  isinf(), the standards merely say that the return value is nonzero
81       if and only if the argument has an infinite value.
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NOTES

84       In glibc 2.01 and earlier, isinf() returns a nonzero  value  (actually:
85       1)  if  x is positive infinity or negative infinity.  (This is all that
86       C99 requires.)
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COLOPHON

92       This page is part of release 4.15 of the Linux  man-pages  project.   A
93       description  of  the project, information about reporting bugs, and the
94       latest    version    of    this    page,    can     be     found     at
95       https://www.kernel.org/doc/man-pages/.
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99                                  2017-09-15                     FPCLASSIFY(3)