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# FPCLASSIFY(3) - man page online | library functions

Floating-point classification macros.

Chapter
2015-08-08
FPCLASSIFY(3)                       Linux Programmer's Manual                       FPCLASSIFY(3)

NAME fpclassify, isfinite, isnormal, isnan, isinf - floating-point classification macros
SYNOPSIS #include <math.h> int fpclassify(x); int isfinite(x); int isnormal(x); int isnan(x); int isinf(x); Link with -lm. Feature Test Macro Requirements for glibc (see feature_test_macros(7)): fpclassify(), isfinite(), isnormal(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99 isnan(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99 isinf(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99
DESCRIPTION Floating point numbers can have special values, such as infinite or NaN. With the macro fpclassify(x) you can find out what type x is. The macro takes any floating-point expres‐ sion as argument. The result is one of the following values: FP_NAN x is "Not a Number". FP_INFINITE x is either positive infinity or negative infinity. FP_ZERO x is zero. FP_SUBNORMAL x is too small to be represented in normalized format. FP_NORMAL if nothing of the above is correct then it must be a normal floating-point number. The other macros provide a short answer to some standard questions. isfinite(x) returns a nonzero value if (fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE) isnormal(x) returns a nonzero value if (fpclassify(x) == FP_NORMAL) isnan(x) returns a nonzero value if (fpclassify(x) == FP_NAN) isinf(x) returns 1 if x is positive infinity, and -1 if x is negative infinity.
ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌─────────────────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├─────────────────────────────┼───────────────┼─────────┤ │fpclassify(), isfinite(), │ Thread safety │ MT-Safe │ │isnormal(), isnan(), isinf() │ │ │ └─────────────────────────────┴───────────────┴─────────┘
CONFORMING TO POSIX.1-2001, POSIX.1-2008, C99. For isinf(), the standards merely say that the return value is nonzero if and only if the argument has an infinite value.
NOTES In glibc 2.01 and earlier, isinf() returns a nonzero value (actually: 1) if x is positive infinity or negative infinity. (This is all that C99 requires.)
SEE ALSO finite(3), INFINITY(3), isgreater(3), signbit(3)
COLOPHON This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.
2015-08-08 FPCLASSIFY(3)
 This manual Reference Other manuals fpclassify(3) referred by finite(3) | INFINITY(3) | isgreater(3) | math_error(7) | nan(3) refer to attributes(7) | feature_test_macros(7) | finite(3) | INFINITY(3) | isgreater(3) | signbit(3)