NAME
nan, nanf,
nanl —
quiet NaNs
LIBRARY
library “libm”
SYNOPSIS
#include
<math.h>
double
nan(const
char *s);
float
nanf(const
char *s);
long double
nanl(const
char *s);
DESCRIPTION
TheNAN macro expands to a quiet NaN (Not A Number).
Similarly, each of the
nan(),
nanf(),
and
nanl()
functions generate a quiet NaN value without raising an invalid exception. The
argument s should point to either an empty string or a
hexadecimal representation of a non-negative integer (e.g.,
"0x1234".) In the latter case, the integer is encoded in some free
bits in the representation of the NaN, which sometimes store machine-specific
information about why a particular NaN was generated. There are 22 such bits
available for float variables, 51 bits for
double variables, and at least 51 bits for a
long double. If s is improperly
formatted or represents an integer that is too large, then the particular
encoding of the quiet NaN that is returned is indeterminate.
COMPATIBILITY
Calling these functions with a non-empty string isn't portable.
Another operating system may translate the string into a different NaN
encoding, and furthermore, the meaning of a given NaN encoding varies across
machine architectures. If you understood the innards of a particular
platform well enough to know what string to use, then you would have no need
for these functions anyway, so don't use them. Use the
NAN macro instead.
SEE ALSO
STANDARDS
The nan(), nanf(),
and nanl() functions and the
NAN macro conform to ISO/IEC
9899:1999 (“ISO C99”).