iserr

Iserr is a term used in software development to describe a predicate, macro, or function intended to determine whether a given value encodes an error condition. It is not a formal language feature, but a naming convention found in various codebases to improve readability when error signaling uses special values rather than exceptions.

Usage patterns vary by language. In C and C-like code, an iserr macro may test for negative return values or a range of error codes. For example, if (ISERR(rc)) { ... } handles errors signaled by a function returning int. In systems like the Linux kernel, error values may be encoded as pointers, and macros such as IS_ERR(ptr) check whether a pointer encodes an error rather than a valid object.

In languages that use exceptions, iserr-style checks are less common, but a function might still return an error object or an optional result, and a predicate like isError(x) or x instanceof Error may be used to test for error presence before taking action.

Benefits of an iserr pattern include explicit, local error checks and easier control flow in function compositions. Drawbacks include inconsistent conventions across a codebase, potential ambiguity when a legitimate value can resemble an error encoding, and the need for clear documentation to avoid misinterpretation.

See also: error handling, error codes, errno, exception handling, error objects.