The InStr function returns the numeric position of the first occurrence of a specified substring within a specified string when starting from the beginning (left end) of the string.

An output of zero indicates no match.

The first argument is optional.

Start

The optional Start argument is the numeric position, counted from the left, which defines where to start the search for the substring. The search proceeds from the left to the right.

There are two mandatory arguments.

String

The String argument is the string in which you will search.

Substring

The Substring argument is the substring you are searching for.

Code:
<% =InStr("ABCDE ABCDE", "C") %>

Output:
3

Code:
<% =InStr(4, "ABCDE ABCDE", "C") %>

Output:
9

The fourth argument is optional.

Compare

The optional Compare argument must only use either the constant or value of the COMPARISON CONSTANTS.

Note that when you use the Compare argument you must use the Start argument.

In the example, by using VBBinaryCompare, or 0, for the Compare argument, all upper/lower case differences are obeyed in the search for the first match.

Code:
<% =InStr(1, "ABCDE ABCDE", "c", 0) %>

Output:
0

In the example, by using VBTextCompare, or 1, for the Compare argument, all upper/lower case differences are ignored in the search for the first match.

Code:
<% =InStr(1, "ABCDE ABCDE", "c", VBTextCompare) %>

Output:
3