nan, nanf, nanl - return 'Not a Number'
These functions return a representation (determined by
of a quiet NaN. If the implementation does not support quiet NaNs, these
functions return zero.
nan("char-sequence") is equivalent to:
tagp is used in an unspecified manner. On IEEE
754 systems, there are many representations of NaN, and
selects one. On other systems it may do nothing.
These functions first appeared in glibc in version 2.1.
C99, POSIX.1-2001, POSIX.1-2008. See also IEC 559 and the appendix with recommended functions in IEEE 754/IEEE 854.
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