Existence detection

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:

<syntaxhighlight lang="vbnet"> 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 </syntaxhighlight>