fpclassify, isfinite, isnormal, isnan, isinf - floating-point classification
macros
Math library (
libm,
-lm)
#include <math.h>
int fpclassify(x);
int isfinite(x);
int isnormal(x);
int isnan(x);
int isinf(x);
fpclassify(),
isfinite(),
isnormal():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
isnan():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
isinf():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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 expression 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.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
fpclassify (), isfinite (), isnormal (), isnan (), isinf () |
Thread safety |
MT-Safe |
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.
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.)
finite(3),
INFINITY(3),
isgreater(3),
signbit(3)