_INSTRREV - QB64Official/qb64 GitHub Wiki

The _INSTRREV function searches for a substring inside another string, but unlike INSTR it searches from right to left.

Syntax

position% = _INSTRREV([start%,] baseString$, subString$)

Parameter(s)

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

Description

• The function returns the position% in the baseString$ where the subString$ was found, from right to left.
• position% will be 0 if the search found no matches in the base string.
• _INSTRREV returns 0 if an empty baseString$ is passed, and returns LEN(baseString$) with an empty subString$.
• The start% position is useful when making multiple searches in the same string. See the example below.
• The subString$ should be smaller or equal in LEN to the baseString$, or 0 is returned.
• A start% value of 0 or less starts search from the end of the baseString$ (same as not passing a start% parameter).

Example(s)

Separating a file name from a full path.

fullPath$ = "C:\Documents and Settings\Administrator\Desktop\qb64\internal\c\libqb\os\win\libqb_1_2_000000000000.o"
file$ = MID$(fullPath$, _INSTRREV(fullPath$, "\") + 1)
PRINT file$

libqb_1_2_000000000000.o

Searching for multiple instances of a substring inside a base string, going from the end to the start.

sentence$ = " This is a string full of spaces, including at start and end... "
PRINT sentence$
DO
    findPrevSpace% = _INSTRREV(findPrevSpace% - 1, sentence$, SPACE$(1))
    IF findPrevSpace% = 0 THEN
        LOCATE 4, 1
        PRINT "No more spaces"
        EXIT DO
    END IF

    LOCATE 2, findPrevSpace%
    PRINT "^"
    totalSpaces = totalSpaces + 1

    IF findPrevSpace% = 1 THEN 
        LOCATE 4, 1
        PRINT "Last space found at position 1"
        EXIT DO
    END IF
LOOP
PRINT "Total spaces found: "; totalSpaces

 This is a string full of spaces, including at start and end... 
^    ^  ^ ^      ^    ^  ^       ^         ^  ^     ^   ^      ^

Last space found at position 1
Total spaces found: 13

See Also

• MID$, INSTR
• SPACE$