ACC: Problems When You Use Instr() to Find Special Characters

ID: Q151164

The information in this article applies to:

Microsoft Access versions 1.0, 1.1, 2.0, 7.0, 97

SYMPTOMS

Moderate: Requires basic macro, coding, and interoperability skills.

When you use the Instr() function, you may see incorrect results when you search through a character string looking for certain ASCII characters, usually non-US characters.

CAUSE

There are two possible causes for this behavior:

The Option Compare Database statement is in effect. This can cause unexpected results when you search for any character whose ASCII value is 128 or greater.
```
    -or-
```

You are searching for certain characters, even with the Option Compare Binary or Option Compare Text statements in effect. These characters are not affected by the Option Compare setting when you use the Instr() function.

These characters include, but are not limited to the following:

      Upper- and lower-case "A" with umlaut     (ASCII 196 and 228)
      Upper- and lower-case "AE"                (ASCII 198 and 230)
      Upper- and lower-case "N" with tilde      (ASCII 209 and 241)
      Upper- and lower-case "O" with umlaut     (ASCII 214 and 246)
      Upper- and lower-case "U" with umlaut     (ASCII 220 and 252)
      German double-"s" "ess-szet" character    (ASCII 223)

The Instr() function incorrectly returns a match on the first alphabetical character that resembles one of these special characters. For example, searching for "A" with an umlaut matches any letter "A."

RESOLUTION

You can use one of the following two methods to work around this behavior.

Method 1

If the incorrect behavior is due to Cause 1 in the "Cause" section, place the Option Compare Binary statement at the top of your module.

Method 2

If the incorrect behavior occurs because you are searching for characters that are not affected by the Option Compare setting, follow the steps below to create a user-defined function to search for the special characters listed in Cause 2 in the "Cause" section.

This method assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to your version of the "Building Applications with Microsoft Access" manual.

NOTE: Visual Basic for Applications is called Access Basic in Microsoft Access versions 1.x and 2.0. For more information about Access Basic, please refer to the "Introduction to Programming" manual in Microsoft Access version 1.x or the "Building Applications" manual in Microsoft Access version 2.0

1. Start Microsoft Access.

2. Open an existing database, or create a new database.

3. Create a new module.

4. Type the following lines in the Declarations section:

      Option Explicit
      Option Compare Database

5. Type the following function:

   NOTE: In the following sample code, an underscore (_) at the end of a
   line is used as a line-continuation character. Remove the underscore
   from the end of the line when re-creating this code in Access Basic.

       Function NewInstr (strSearch As String, strWhat As String) As _
       Integer
       '
       ' This function searches for the character strWhat in the string
       ' strSearch. It uses the ASCII value of strWhat, and therefore is
       ' not subject to Microsoft Access translation of special characters
       ' and ligatures. It returns the integer position of the strWhat in
       ' strSearch. It returns 0 if either strSearch or strWhat is empty,
       ' or if strWhat cannot be found.
       '
       ' Note: If strWhat contains more than one character, only the first
       ' character is searched for.

       Dim iLen As Integer, i As Integer
       Dim iRetVal As Integer

       If IsNull(strSearch) Or IsNull(strWhat) Or _
       IsEmpty(strSearch) Or IsEmpty(strWhat) Then
          iRetVal = 0
       Else
          iRetVal = 0
          iLen = Len(strSearch)
          i = 1
          Do
             If Asc(Mid(strSearch, i, 1)) = Asc(strWhat) Then
                iRetVal = I
             End If
             i = i + 1
          Loop While iRetVal = 0 And i <= iLen
       End If
       NewInstr = iRetVal

       End Function

6. Open the Debug window (called the Immediate window in Microsoft Access

   versions 1.x and 2.0), type the following line, and then press ENTER:

      ? NewInstr(Chr(223),Chr(223))

   Note that the result, 1, appears on the next line.

   NOTE: You can generate the special characters directly by holding down
   the ALT key on your keyboard, typing the number 0 (zero) on the numeric
   keypad, followed by the ASCII code, and then releasing the ALT key.
   Make sure that NumLock is on before typing this. For example, to
   generate the ess-szet character, hold down the ALT key and type 0223 on
   the numeric keypad.

7. Type the following line in the Debug window, and then press ENTER:

      ? NewInstr(Chr(223),"s")

   The result, 0, appears on the next line.

MORE INFORMATION

Steps to Reproduce Behavior

1. Start Microsoft Access and open the sample database Northwind.mdb

   (called NWIND.MDB in Microsoft Access 1.x and 2.0).

2. Create a new module.

3. Type the following lines in the Declarations section if they are not

   already there:

      Option Explicit
      Option Compare Database

4. In the Debug window, type the following line, and then press ENTER:

      ? Instr(Chr(223),"s")

   Note that the incorrect result, 1, appears on the next line.

REFERENCES

For more information about Option Compare Database, search the Help Index for "Option Compare Statement," or ask the Microsoft Access 97 Office Assistant.

Additional query words:

Keywords          : kbprg
Version           : 1.0 1.1 2.0 7.0 97
Platform          : WINDOWS
Hardware          : x86
Issue type        : kbprb

Last Reviewed: January 7, 1999