nan man page


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

nan, nanf, nanl — return quiet NaN


#include <math.h>

double nan(const char *tagp);
float nanf(const char *tagp);
long double nanl(const char *tagp);


The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2008 defers to the ISO C standard.

The function call nan("n-char-sequence") shall be equivalent to:

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

The function call nan("") shall be equivalent to:

strtod("NAN()", (char **) NULL)

If tagp does not point to an n-char sequence or an empty string, the function call shall be equivalent to:

strtod("NAN", (char **) NULL)

Function calls to nanf() and nanl() are equivalent to the corresponding function calls to strtof() and strtold().

Return Value

These functions shall return a quiet NaN, if available, with content indicated through tagp.

If the implementation does not support quiet NaNs, these functions shall return zero.


No errors are defined.

The following sections are informative.

See Also


The Base Definitions volume of POSIX.1‐2008, <math.h>


2013 IEEE/The Open Group POSIX Programmer's Manual