nan(), nanf(), nanl()

Updated: April 19, 2023

Return a quiet NaN


#include <math.h>

double nan( const char *tagp );

float nanf( const char *tagp );

long double nanl( const char *tagp );


NULL, or an n-char sequence that identifies the contents of a NaN.


The general-purpose math library.
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.


The nan(), nanf(), and nanl() functions convert the string pointed to by tagp into a quiet NaN, if available.

Calls to nan() are equivalent to calls to strtod(), as shown below:

This call: Is equivalent to:
nan("n-char-sequence") strtod("NAN(n-char-sequence)", (char **) NULL)
nan("") strtod("NAN()", (char **) NULL)
nan(tagp), where tagp doesn't point to an n-char sequence or an empty string strtod("NAN", (char **) NULL)
Note: The QNX Neutrino versions of these functions don't interpret n-char sequences, and the results are equivalent to specifying NULL for tagp.

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


A quiet NaN, if available, corresponding to the string pointed to by tagp.


C11, POSIX 1003.1

Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes