nan, nanf, nanl - return quiet NaN
double nan(const char *tagp);
float nanf(const char *tagp);
long double nanl(const char *tagp);
[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.1-2017 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().
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.
First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.
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