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.
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(7).
┌────────────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────┼───────────────┼────────────────┤
│ nan(), nanf(), nanl() │ Thread safety │ MT-Safe locale │
└────────────────────────────────────┴───────────────┴────────────────┘
STANDARDS
C11, POSIX.1-2008.
See also IEC 559 and the appendix with recommended functions in IEEE
754/IEEE 854.
HISTORY
glibc 2.1. C99, POSIX.1-2001.
SEE ALSO
isnan(3), strtod(3), math_error(7)
Linux man-pages 6.7 2023-10-31 nan(3)
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