NAME

nan, nanf, nanl — return quiet NaN

SYNOPSIS

#include <math.h>

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


DESCRIPTION

^[CX] 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.1-2024 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.

^[MX] The returned value shall be exact and shall be independent of the current rounding direction mode.

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

ERRORS

No errors are defined.

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

strtod

XBD <math.h>

CHANGE HISTORY

First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

Issue 8

Austin Group Defect 1302 is applied, aligning these functions with the ISO/IEC 9899:2018 standard.