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Existence checking or existence detection is an important aspect of many computer programs. An existence check before reading a file can catch and/or prevent a fatal error, for instance. For that reason, most programming language libraries contain a means of checking whether a file exists.
An existence check can sometimes involve a "brute force" approach of checking all records for a given identifier, as in this Microsoft Excel Visual Basic for Applications code for detecting whether a worksheet exists:
FunctionSheetExists(sheetNameAsString)AsBooleanDimsheetCountAsIntegerDimtAsIntegerSheetExists=FalsesheetCount=ActiveWorkbook.Sheets.CountFort=1TosheetCountIfSheets(t).Name=sheetNameThenSheetExists=TrueExitFunctionEndIfNexttEndFunction
