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.
nan, nanf, nanl — 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.1‐2008 defers to the ISO C standard.
The function call nan("n-char-sequence") shall be equivalent to:
The function call nan("") shall be equivalent to:
strtod("NAN(n-char-sequence)", (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().
These functions shall return a quiet NaN, if available, with content indicated through tagp.
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.1‐2008, <math.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 http://www.unix.org/online.html .
strtod("NAN", (char **) NULL)
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