INSTR - QB64Official/qb64 GitHub Wiki

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

Syntax

position% = INSTR([start%,] baseString$, searchString$)

Parameter(s)

  • The optional literal or variable INTEGER start% indicates where in the baseString$ the search must start.
  • The baseString$ is a literal or variable STRING value to be searched for an exact match including UCASE$.
  • The searchString$ is a literal or variable STRING value being searched.

Description

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

QBasic

  • The start% position had to be at least 1 or greater when used or there will be an ERROR Codes error. In QB64, a start% value of 0 or negative is interpreted as 1 and doesn't generate an error.

Example(s)

Reading more than one instance of a word in a string using the INSTR return value as the start value plus 1.


text$ = "The cats and dogs where playing, even though dogs don't like cats."
DO
  findcats% = INSTR(findcats% + 1, text$, "cats") ' find another occurance after
  IF findcats% THEN PRINT "There is 'cats' in the string at position:"; findcats%
LOOP UNTIL findcats% = 0

findmonkey% = INSTR(text$, "monkeys")  ' find any occurance?
PRINT findmonkey%; "'monkeys' were found so it returned:"; findmonkey% 



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

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.

See Also