nan, nanf, nanl - return 'Not a Number'
These functions return a representation (determined by
tagp) 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
tagp 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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