The Open Group Base Specifications Issue 7, 2018 edition

IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)

Copyright © 2001-2018 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.1-2017 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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