Section: POSIX Programmer's Manual (3P)
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.
--- return quiet NaN
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.1-2017 defers to the ISO C standard.
The function call nan("n-char-sequence") shall be
strtod("NAN(n-char-sequence)", (char **) NULL);
The function call nan("") shall be equivalent to:
strtod("NAN()", (char **) NULL)
does not point to an
sequence or an empty string, the function call shall be equivalent to:
strtod("NAN", (char **) NULL)
Function calls to
are equivalent to the corresponding function calls to
These functions shall return a quiet NaN, if available, with content
If the implementation does not support quiet NaNs, these functions
shall return zero.
No errors are defined.
The following sections are informative.
The Base Definitions volume of POSIX.1-2017,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
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