In computer programming, a variable that stores error codes when system calls or library functions fail. A debugging tool that helps identify what went wrong.
Contraction of 'error number', from English 'error' (Latin 'errare', to wander) + 'number'. Introduced in early Unix systems in the 1970s as a standardized way to report system errors.
Errno represents programming's attempt to make failures meaningful - instead of just crashing, systems learned to whisper their problems through numbered codes. It's like giving computers a vocabulary for their pain, turning mysterious crashes into specific, diagnosable conditions.
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