Linux manual pages Section 3  

Name

nan, nanf, nanl — return 'Not a Number'

Synopsis

#include <math.h>
double nan( const char *tagp);
 
float nanf( const char *tagp);
 
long double nanl( const char *tagp);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
nan(), nanf(), nanl():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE;
or cc -std=c99
[Note] Note

Link with −lm.

DESCRIPTION

These functions return a representation (determined by tagp) of a quiet NaN. If the implementation does not support quiet NaNs, these functions 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 systems, there are many representations of NaN, and tagp selects one. On other systems it may do nothing.

VERSIONS

These functions first appeared in glibc in version 2.1.

CONFORMING TO

C99, POSIX.1-2001. See also IEC 559 and the appendix with recommended functions in IEEE 754/IEEE 854.

SEE ALSO

isnan(3), strtod(3), math_error(7)

COLOPHON

This page is part of release 3.24 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


  Copyright 2002 Walter Harms (walter.harmsinformatik.uni-oldenburg.de)
Distributed under GPL
Based on glibc infopages

Corrections by aeb