@node nan, math
@findex nan
@subheading Syntax

@example
#include <math.h>

double nan(const char *tagp);
@end example

@subheading Description

@code{nan} returns a quiet NaN with contents indicated by @var{tagp}.

@subheading Return Value

The quiet NaN.

If quiet NaNs are not supported, zero is returned. DJGPP supports
quiet NaNs.

@subheading Portability

@portability !ansi-c89, ansi-c99

@subheading Example

@example
double d = nan("0x1234");
@end example