nan(3) Library Functions Manual nan(3)
NAME
nan, nanf, nanl - return 'Not a Number'
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>
double nan(const char *tagp);
float nanf(const char *tagp);
long double nanl(const char *tagp);
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 func-
tions 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 sys-
tems, there are many representations of NaN, and tagp selects one. On
other systems it may do nothing.
VERSIONS
These functions were added in glibc 2.1.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌─────────────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼────────────────┤
│nan(), nanf(), nanl() │ Thread safety │ MT-Safe locale │
└─────────────────────────────────────┴───────────────┴────────────────┘
STANDARDS
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)
Linux man-pages 6.03 2022-12-15 nan(3)
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