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():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
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:
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.
These functions first appeared in glibc in version 2.1.
C99, POSIX.1-2001. See also IEC 559 and the appendix with recommended
functions in IEEE 754/IEEE 854.
isnan(3), strtod(3), math_error(7)
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