NAN(3) Linux Programmers Manual NAN(3)
nan, nanf, nanl - return Not a Number
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; or
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) and similarly calls to nanf() and nanl() are equiva
lent 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.
C99. 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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be found at http://www.kernel.org/doc/man-pages/.
GNU 2008-07-23 NAN(3)