#include <math.h>

       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:

           strtod("NAN(char-sequence)", NULL);

       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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GNU                               2010-09-20                            NAN(3)
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