.SH SYNOPSIS
.nf
.B #include <math.h>
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.BI "double nan(const char *" tagp );
.BI "float nanf(const char *" tagp );
.BI "long double nanl(const char *" tagp );
.fi
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.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
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.BR nan (),
.BR nanf (),
.BR nanl ():
of a quiet NaN.
If the implementation does not support
quiet NaNs, these functions return zero.
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The call
.I nan("char\-sequence")
is equivalent to:
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.in +4n
.EX
strtod("NAN(char\-sequence)", NULL);
.EE
.in
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Similarly, calls to
.BR nanf ()
and
.BR strtof (3)
and
.BR strtold (3).
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The argument
.I tagp
is used in an unspecified manner.
.TE
.SH STANDARDS
C11, POSIX.1-2008.
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See also IEC 559 and the appendix with
recommended functions in IEEE 754/IEEE 854.
.SH HISTORY