_isnan, _isnanl

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Header File

float.h

Prototype

int _isnan(double d);
int _isnanl(long double ld);

Description

Tests whether a given double-precision floating-point value d is a NaN.

_isnanl is the long double version; it takes a long double argument.

Return Value

Returns a nonzero value (TRUE) if the value passed in is a NaN; otherwise it returns 0 (FALSE). The non-zero return value corresponds to either _FPCLASS_SNAN, if the NaN is of the signaling type, or _FPCLASS_QNAN, if the NaN is of the quiet type. The values for _FPCLASS_SNAN and _FPCLASS_QNAN are in float.h.

	POSIX	ANSI C	ANSI C++	Win32	Win64	macOS
_isnan				+
_isnanl				+

Example

#include <math.h>

int print_double(double value) {
	/* print "Infinite" if value is NaN */
	if (_isnan(value))
		printf("Infinite");
	else
		printf("%f", value);
}