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:

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

See also

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