Instr function

Returns a Variant (Long) specifying the position of the first occurrence of one string within another.

See some examples

Syntax

InStr ([start, ] string1, string2 [, compare ] )

The InStr function syntax has these arguments:

Argument	Description
start	Optional. Numeric expression that sets the starting position for each search. If omitted, search begins at the first character position. If start contains Null, an error occurs. The start argument is required if compare is specified.
string1	Required. String expression being searched.
string2	Required. String expression sought.
compare	Optional. Specifies the type of string comparison. If compare is Null, an error occurs. If compare is omitted, the OptionCompare setting determines the type of comparison. Specify a valid LCID (LocaleID) to use locale-specific rules in the comparison.

Tip:  In Access 2010, the Expression Builder has IntelliSense, so you can see what arguments your expression requires. 

Settings

The compare argument settings are:

Constant	Value	Description
vbUseCompareOption	-1	Performs a comparison using the setting of the Option Compare statement.
vbBinaryCompare	0	Performs a binary comparison.
vbTextCompare	1	Performs a textual comparison.
vbDatabaseCompare	2	Microsoft Office Access 2007 only. Performs a comparison based on information in your database.

Return Values

If	InStr returns
string1 is zero-length	0
string1 is Null	Null
string2 is zero-length	start
string2 is Null	Null
string2 is not found	0
string2 is found within string1	Position at which match is found
start > string2	0

Remarks

The InStrB function is used with byte data contained in a string. Instead of returning the character position of the first occurrence of one string within another, InStrB returns the byte position.

Examples

Use the InStr function in an expression    You can use InStr wherever you can use expressions. For example, if you want to find the position of the first period (.) in a field that contains IP addresses (named IPAddress), you can use InStr to find it, like so:

InStr(1,[IPAddress],".")

The InStr function examines each value in the IPAddress field and returns the position of the first period. Hence, if the first portion of the IP address is 10., the function returns the value 3.

You can then use other functions, operating on the output of the InStr function, to extract the portion of the IP address that precedes the first period, like so:

Left([IPAddress],(InStr(1,[IPAddress],".")-1))

In this example, InStr(1,[IPAddress],".") returns the position of the first period. Subtracting 1 determines how many characters precede the first period, in this case, 2. The Left function then extracts that many characters from the left portion of the IPAddress field, returning the value 10.

Use InStr in VBA code    

Note: Examples that follow demonstrate the use of this function in a Visual Basic for Applications (VBA) module. For more information about working with VBA, select Developer Reference in the drop-down list next to Search and enter one or more terms in the search box.

This example uses the InStr function to return the position of the first occurrence of one string within another.

Dim SearchString, SearchChar, MyPos
SearchString ="XXpXXpXXPXXP"    ' String to search in.
SearchChar = "P"    ' Search for "P".
' A textual comparison starting at position 4. Returns 6.
MyPos = Instr(4, SearchString, SearchChar, 1)    
' A binary comparison starting at position 1. Returns 9.
MyPos = Instr(1, SearchString, SearchChar, 0)
' Comparison is binary by default
' (last argument is omitted).
MyPos = Instr(SearchString, SearchChar)    ' Returns 9.
MyPos = Instr(1, SearchString, "W")    ' Returns 0.

String functions and how to use them