fpclassify(3)

1fpclassify(3)              Library Functions Manual              fpclassify(3)
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NAME

6       fpclassify, isfinite, isnormal, isnan, isinf - floating-point classifi‐
7       cation macros
8

LIBRARY

10       Math library (libm, -lm)
11

SYNOPSIS

13       #include <math.h>
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15       int fpclassify(x);
16       int isfinite(x);
17       int isnormal(x);
18       int isnan(x);
19       int isinf(x);
20
21   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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23       fpclassify(), isfinite(), isnormal():
24           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
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26       isnan():
27           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
28               || _XOPEN_SOURCE
29               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
30               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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32       isinf():
33           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
34               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
35               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

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

67       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
68       tributes(7).
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70       ┌────────────────────────────────────────────┬───────────────┬─────────┐
71       │Interface                                   │ Attribute     │ Value   │
72       ├────────────────────────────────────────────┼───────────────┼─────────┤
73       │fpclassify(), isfinite(), isnormal(),       │ Thread safety │ MT-Safe │
74       │isnan(), isinf()                            │               │         │
75       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

78       C11, POSIX.1-2008.
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HISTORY

81       POSIX.1-2001, C99.
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83       In  glibc  2.01 and earlier, isinf() returns a nonzero value (actually:
84       1) if x is positive infinity or negative infinity.  (This is  all  that
85       C99 requires.)
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NOTES

88       For  isinf(), the standards merely say that the return value is nonzero
89       if and only if the argument has an infinite value.
90