The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group

#### NAME

> isless - test if x is less than y

#### SYNOPSIS

> ``#include <math.h>
> int isless(real-floating` x`, real-floating` y`);
> ``

#### DESCRIPTION

> [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.1-2008 defers to the ISO C standard.

> The isless() macro shall determine whether its first argument is less than its second argument. The value of isless(x, y) shall be equal to (x) < (y); however, unlike (x) < (y), isless(x, y) shall not raise the invalid floating-point exception when x and y are unordered.

#### RETURN VALUE

> Upon successful completion, the isless() macro shall return the value of (x) < (y).

> If x or y is NaN, 0 shall be returned.

#### ERRORS

> No errors are defined.

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> The relational and equality operators support the usual mathematical relationships between numeric values. For any ordered pair of numeric values, exactly one of the relationships (less, greater, and equal) is true. Relational operators may raise the invalid floating-point exception when argument values are NaNs. For a NaN and a numeric value, or for two NaNs, just the unordered relationship is true. This macro is a quiet (non-floating-point exception raising) version of a relational operator. It facilitates writing efficient code that accounts for NaNs without suffering the invalid floating-point exception. In the SYNOPSIS section, real-floating indicates that the argument shall be an expression of real-floating type.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> isgreater, isgreaterequal, islessequal, islessgreater, isunordered

> XBD <math.h>

#### CHANGE HISTORY

> First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

End of informative text.

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