===== Instrx (Function) =====
==== Format ====
**instrx** ( [[stringexpressions|haystack_string_expression]] , [[regularexpressions|regular_expression]] )\\
**instrx** ( [[stringexpressions|haystack_string_expression]] , [[regularexpressions|regular_expression]] , [[integerexpressions|start_expression]] )

returns [[integerexpressions|integer_expression]]

==== Description ====
Check to see if the text represented by the regular expression [[regularexpressions|regular_expression]] is contained in the string [[stringexpressions|haystack_string_expression]].  If it is, then this function will return the index of starting character of the first place where [[stringexpressions|needle_string_expression]] occurs.  Otherwise, this function will return 0.

You may optionally specify a starting location for the search to begin [[integerexpressions|start_expression]].  If the start is 1 or greater the search will begin from the specified character from the start.  If the start is < 0 then the search will begin from the nth character from the end.  The search will ALWAYS look forward.

==== Note ====
String indices begin at 1.

==== Example ====
<code>
print instrx("HeLLo", "[Ll]o")
print instrx("Hello, Kitti","[Ii]",10)
</code>
will display
<code>
4
12
</code>

==== Notes ====

**instrx** can be used to test if a string matches a regular expression.  In for following example the function isnumber returns true if the string passed is in for format of a floating point number and false if not. 
<code>
function isnumber(s$)
   # return true if a number - false of not
   return instrx(s$,"^-?\d+\.?\d*$") <> 0
end function
</code>

By default the nature of regular expressions is "greedy". This behaviour can be changed using the [[regexminimal|RegexMinimal]] statement.

==== See Also ====
{{page>en:start#String Handling&noheader}}

==== History ==== 
|0.9.6.56|New To Version|
|1.99.99.53|Added start position < 0|