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NAN(3) Linux Programmer's 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 || _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 functions 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
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.
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
isnan(3), strtod(3), math_error(7)
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GNU 2010-09-20 NAN(3)
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