fpclassify(3) Library Functions Manual fpclassify(3)

# NAME¶

fpclassify, isfinite, isnormal, isnan, isinf - floating-point classification macros

# LIBRARY¶

Math library (libm, -lm)

# SYNOPSIS¶

`#include <math.h>`
```int fpclassify(x);
int isfinite(x);
int isnormal(x);
int isnan(x);
int isinf(x);```

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

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```

# 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 expression as argument. The result is one of the following values:

x is "Not a Number".
x is either positive infinity or negative infinity.
x is zero.
x is too small to be represented in normalized format.
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.

returns a nonzero value if
(fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)
returns a nonzero value if (fpclassify(x) == FP_NORMAL)
returns a nonzero value if (fpclassify(x) == FP_NAN)
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 (), isnormal (), isnan (), isinf () Thread safety MT-Safe

# STANDARDS¶

C11, POSIX.1-2008.

# HISTORY¶

POSIX.1-2001, C99.

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.)

# NOTES¶

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