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{{Not a typo|.}}Count
For t = 1 To  sheetCount
If Sheets(t).Name = sheetName Then
SheetExists = True
Exit Function
End If
Next t
End Function