nan

Section: C Library Functions (3)
Updated: 2022-12-15
Index Return to Main Contents
 

NAME

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

LIBRARY

Math library (libm, -lm)  

SYNOPSIS

#include <math.h>

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

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

nan(), nanf(), nanl():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
 

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 were added in glibc 2.1.  

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
nan(), nanf(), nanl() Thread safetyMT-Safe locale

 

STANDARDS

C99, POSIX.1-2001, POSIX.1-2008. See also IEC 559 and the appendix with recommended functions in IEEE 754/IEEE 854.  

SEE ALSO

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


 

Index

NAME
LIBRARY
SYNOPSIS
DESCRIPTION
VERSIONS
ATTRIBUTES
STANDARDS
SEE ALSO

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