The [[INSTR]] function searches for the first occurence of a search [[STRING]] within a base string and returns the position it was found.


{{PageSyntax}}
: {{Parameter|position%}} = [[INSTR]]([{{Parameter|start%}},] {{Parameter|baseString$}}, {{Parameter|searchString$}})


{{Parameters}}
* The optional literal or variable [[INTEGER]] {{Parameter|start%}} indicates where in the {{Parameter|baseString$}} the search must start. 
* The {{Parameter|baseString$}} is a literal or variable [[STRING]] value to be searched for an exact match including [[UCASE$|letter cases]]. 
* The {{Parameter|searchString$}} is a literal or variable [[STRING]] value being searched.


{{PageDescription}}
* The function returns the {{Parameter|position%}} in the {{Parameter|baseString$}} where the {{Parameter|searchString$}} was found.
* {{Parameter|position%}} will be 0 if the search found no matches in the base string. 
* [[INSTR]] returns 0 if an empty {{Parameter|baseString$}} is passed, and returns 1 with an empty {{Parameter|searchString$}}.
* The {{Parameter|start%}} position is useful when making multiple searches in the same string. See the example below.
* The {{Parameter|searchString$}} should be smaller or equal in [[LEN|length]] to the {{Parameter|baseString$}}, or 0 is returned.
* Non-zero {{Parameter|position%}} return values can be used as a new start position by adding 1 to re-search the base string. See the example below.
* In a loop, INSTR can search an entire file for occurences of certain words. See the [[MID$ (statement)|MID$]] statement example.


==QBasic/QuickBASIC==
* The {{Parameter|start%}} position had to be at least 1 or greater when used or there will be an [[ERROR Codes|Illegal function call]] error. In '''QB64''', a {{Parameter|start%}} value of 0 or negative is interpreted as 1 and doesn't generate an error.


{{PageExamples}}
''Example:'' Reading more than one instance of a word in a string using the INSTR return value as the start value plus 1.
{{CodeStart}} '' ''
text$ = "The cats and dogs where playing, even though dogs don't like cats."
{{Cl|DO...LOOP|DO}}
  findcats% = {{Cl|INSTR}}(findcats% + 1, text$, "cats") ' find another occurance after
  {{Cl|IF...THEN|IF}} findcats% {{Cl|THEN}} {{Cl|PRINT}} "There is 'cats' in the string at position:"; findcats%
{{Cl|LOOP}} {{Cl|UNTIL}} findcats% = 0

findmonkey% = {{Cl|INSTR}}(text$, "monkeys")  ' find any occurance?
PRINT findmonkey%; "'monkeys' were found so it returned:"; findmonkey% '' ''
{{CodeEnd}}
{{OutputStart}}There is 'cats' in the string at position: 5
There is 'cats' in the string at position: 62
 0 'monkeys' were found so INSTR returned: 0
{{OutputEnd}}
: ''Explanation:'' When the INSTR return value is 0 there are no more instances of a string in a string so the search loop is exited.


{{PageSeeAlso}}
* [[MID$]], [[MID$ (statement)]]
* [[LEFT$]], [[RIGHT$]]
* [[LCASE$]], [[UCASE$]]
* [[STRING]], [[INTEGER]]


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