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56 lines
2.9 KiB
Plaintext
56 lines
2.9 KiB
Plaintext
The [[INSTR]] function searches for the first occurence of a search [[STRING]] within a base string and returns the position it was found.
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{{PageSyntax}}
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: {{Parameter|position%}} = [[INSTR]]([{{Parameter|start%}},] {{Parameter|baseString$}}, {{Parameter|searchString$}})
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{{Parameters}}
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* The optional literal or variable [[INTEGER]] {{Parameter|start%}} indicates where in the {{Parameter|baseString$}} the search must start.
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* The {{Parameter|baseString$}} is a literal or variable [[STRING]] value to be searched for an exact match including [[UCASE$|letter cases]].
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* The {{Parameter|searchString$}} is a literal or variable [[STRING]] value being searched.
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{{PageDescription}}
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* The function returns the {{Parameter|position%}} in the {{Parameter|baseString$}} where the {{Parameter|searchString$}} was found.
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* {{Parameter|position%}} will be 0 if the search found no matches in the base string.
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* [[INSTR]] returns 0 if an empty {{Parameter|baseString$}} is passed, and returns 1 with an empty {{Parameter|searchString$}}.
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* The {{Parameter|start%}} position is useful when making multiple searches in the same string. See the example below.
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* The {{Parameter|searchString$}} should be smaller or equal in [[LEN|length]] to the {{Parameter|baseString$}}, or 0 is returned.
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* 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.
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* In a loop, INSTR can search an entire file for occurences of certain words. See the [[MID$ (statement)|MID$]] statement example.
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==QBasic/QuickBASIC==
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* The {{Parameter|start%}} position had to be at least 1 or greater when used or there will be an [[ERROR Codes|Illegal function call]] error. In '''QB64''', a {{Parameter|start%}} value of 0 or negative is interpreted as 1 and doesn't generate an error.
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{{PageExamples}}
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''Example:'' Reading more than one instance of a word in a string using the INSTR return value as the start value plus 1.
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{{CodeStart}} '' ''
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text$ = "The cats and dogs where playing, even though dogs don't like cats."
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{{Cl|DO...LOOP|DO}}
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findcats% = {{Cl|INSTR}}(findcats% + 1, text$, "cats") ' find another occurance after
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{{Cl|IF...THEN|IF}} findcats% {{Cl|THEN}} {{Cl|PRINT}} "There is 'cats' in the string at position:"; findcats%
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{{Cl|LOOP}} {{Cl|UNTIL}} findcats% = 0
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findmonkey% = {{Cl|INSTR}}(text$, "monkeys") ' find any occurance?
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PRINT findmonkey%; "'monkeys' were found so it returned:"; findmonkey% '' ''
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{{CodeEnd}}
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{{OutputStart}}There is 'cats' in the string at position: 5
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There is 'cats' in the string at position: 62
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0 'monkeys' were found so INSTR returned: 0
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{{OutputEnd}}
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: ''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.
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{{PageSeeAlso}}
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* [[MID$]], [[MID$ (statement)]]
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* [[LEFT$]], [[RIGHT$]]
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* [[LCASE$]], [[UCASE$]]
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* [[STRING]], [[INTEGER]]
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{{PageNavigation}}
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