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Language: Visual Basic
Expertise: Intermediate
Feb 24, 2000



Application Security Testing: An Integral Part of DevOps

Test for Illegal Characters

Use this fast function to test for the occurrence of nonalphanumeric characters in a string:
Private Declare Function StrSpn Lib "SHLWAPI" Alias _
	"StrSpnW" (ByVal psz As Long, ByVal pszSet As Long) As Long
Public Function IsAlphaNum(ByVal sString As String) As Boolean
	Dim lPos As Long
	Const ALPHA_NUM As String = "abcdefgihjklmnopqrstuvwxyz" & _
	' Returns the first occurrence of nonmatching characters
	lPos = StrSpn(StrPtr(pString), StrPtr(pAlphaNum))
	' If the return position is not equal to the length of the 
	' input string, nonalphanumeric chars were found.
	IsAlphaNum = (lPos = Len(sString))
End Function
You can easily modify this function to scan for invalid characters by editing the ALPHA_NUM constant so it includes only characters you consider legal.

Editor's Note: The StrSpn function relies on the version of shlwapi.dll that ships with Internet Explorer 4.0 and later. Handle errors—and expectations—accordingly.
Geir Arnesen
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