Existence detection

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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:

Function SheetExists(sheetName As String) As Boolean     Dim sheetCount As Integer     Dim t As Integer      SheetExists = False     sheetCount = ActiveWorkbook.Sheets.Count     For t = 1 To sheetCount         If Sheets(t).Name = sheetName Then             SheetExists = True             Exit Function         End If     Next t End Function 

• Time-of-check to time-of-use (TOC/TOU)

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