INSTR

Search for an occurrence of a substring within a string.

Syntax

INSTR { startIndex% }, string$, substring$ OUT index%

INSTR will return only the index of the first occurrence of substring$ it finds, starting from the startIndex%. If starIndex% is omitted, then the search starts from the beginning of string$ (index 0). If substring$ is not found, then index% will be -1.

Examples

'find the letter 'a' within this string.
PRINT INSTR("The quick brown fox jumps over the lazy dog.","a")  '36

'find the first "chuck" starting at character 40
CONST #CHUCK="How much wood could a woodchuck chuck if a woodchuck could chuck wood?"
INSTR 40,#CHUCK,"chuck" OUT I%
PRINT I%  '47

'this match will fail
PRINT INSTR("######","!")  '-1

Notes

Empty Substring

If substring$ is empty, every index in any string$ will match it.

'these all match
PRINT INSTR("Hello, world!","")    '0
PRINT INSTR(3,"Hello, world!","")  '3
PRINT INSTR(7,"Hello, world!","")  '7

An interesting quirk of this is that the empty string will match at one index past the end of the string.

'3 is one past the end of the string
PRINT INSTR(3,"ABC","")  '3
PRINT INSTR(4,"ABC","")  '-1