notfound

NOTFOUND is a commonly used sentinel value in computing to indicate that a requested item or result could not be located. It is not a formal standard or protocol, but rather a label applied in various codebases, libraries, and data processing pipelines to signal absence or failure to locate something. The actual representation of NOTFOUND can vary; it may be a specific string such as "NOT FOUND," a numeric sentinel like -1, or a null-equivalent value defined by a programming language or API.

In programming contexts, NOTFOUND is often returned by search functions, lookups, or parsers when no match is found. It can also appear as a constant used to distinguish between found items and missing ones, especially in legacy code or APIs that predate more modern error-handling conventions. In user interfaces, NOTFOUND may be displayed to indicate that data is unavailable or a query yielded no results.

In web and networking contexts, the related concept is HTTP status 404 Not Found, which standardizes the absence of a requested resource on the web. NOTFOUND as a local sentinel value is language- or library-specific, whereas 404 is a universal standard across the World Wide Web.

Considerations and best practices: using a generic sentinel like NOTFOUND can lead to ambiguity if legitimate data can take on that value. Modern approaches favor explicit error handling or nullable/optional types (for example, Optional, Maybe, or null/nil) and clear exceptions. When used, NOTFOUND should be well-documented to avoid misinterpretation across components or teams. See also: null, nil, sentinel value, optional type, 404 Not Found.