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NAN(3) Linux Programmer's Manual NAN(3)
NAME
nan, nanf, nanl - return 'Not a Number'
SYNOPSIS
#include <math.h>
double nan(const char *tagp);
float nanf(const char *tagp);
long double nanl(const char *tagp);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
nan(), nanf(), nanl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
DESCRIPTION
These functions return a representation (determined by tagp) of a quiet NaN. If the implementation does not support quiet NaNs, these functions return zero.
The call nan("char-sequence") is equivalent to:
strtod("NAN(char-sequence)", NULL);
Similarly, calls to nanf() and nanl() are equivalent to analogous calls to strtof(3) and strtold(3).
The argument tagp is used in an unspecified manner. On IEEE 754 systems, there are many representations of NaN, and tagp selects one. On other systems it may
do nothing.
VERSIONS
These functions first appeared in glibc in version 2.1.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
│nan(), nanf(), nanl() │ Thread safety │ MT-Safe locale │
└───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008. See also IEC 559 and the appendix with recommended functions in IEEE 754/IEEE 854.
SEE ALSO
isnan(3), strtod(3), math_error(7)
GNU 2021-03-22 NAN(3)