Legacy Document

relation

You can use the relation function to determine the relationship (less than, greater than, equal to, or unordered) between two real numbers.

relop relation (double_t x, double_t y);

x

Any floating-point number.

y

Any floating-point number.

DESCRIPTION

The relation function returns the relationship between its two arguments.

The relation function is type relop, which is an enumerated type. This function returns one of the following values:

if x > y	GREATERTHAN
if x < y	LESSTHAN
if x = y	EQUALTO
if x or y is a NaN	UNORDERED

Programs can use the result of this function in expressions to test for combinations not supported by the comparison operators, such as "less than or unordered."

EXCEPTIONS

When x and y are finite and nonzero, the result of $relation(x,y)$ is exact.

SPECIAL CASES

Table 10-4 shows the results when one of the arguments to the relation function is a zero, a NaN, or an Infinity. In this table, x and y are finite, nonzero floating-point numbers.

Special cases for the relation function

Operation	Result	Exceptions raised
$relation(+0,y)$	< if y > 0	None
	> if y < 0	None
$relation(x,+0)$	> if x > 0	None
	< if x < 0	None
$relation(-0,y)$	< if y > 0	None
	> if y < 0	None
$relation(x,-0)$	> if x > 0	None
	< if x < 0	None
$relation(+0,-0)$	=	None
$relation(NaN,y)$	Unordered	None[25]
$relation(x,NaN)$	Unordered	None[25]
$relation(+$ ,y)	>	None
$relation(x,+$ )	<	None
$relation(+$ ,+ )	=	None
$relation(-$ ,y)	<	None
$relation(x,-$ )	>	None
$relation(-$ ,- )	=	None

EXAMPLES

r = relation(x, y);
if ((r == LESSTHAN) || (r == UNORDERED))
   printf("No, y is not greater than x.\n");

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[25] If the NaN is a signaling NaN, the invalid exception is raised.