Search string-1 in string-2 gives wrong results.

Question

Hi,
I am searching for the string 'COM' in the sentence
below.
I am getting the string positons of string "COM"
as 1 and 16.
It Should be 1 and 19.
thanks
sharath
SET SERVEROUTPUT ON
DECLARE
str VARCHAR2(200):='COM-1 Hello world COM-1 speaking';
pos NUMBER ;
ps NUMBER :=0 ;
srch VARCHAR2(20) :='COM' ;
BEGIN
While( ps <= length(str))
Loop
pos := instr(str,srch);
If pos > 0 then -- found string COM
str := substr(str,pos + length(srch));
dbms_output.put_line('COM found in pos ==> ' || pos );
End If;
ps := ps + 1;
END LOOP;
END;

Answer 1

I believe the problem is that you are redefining the variable str within your loop. Once you find the first occurrence of "COM" in the string, you modify the string to remove that occurrence and then search again. The logic of your stored procedure is
Loop 1:
str = "COM-1 Hello world COM-1 speaking"
- first occurrence of COM is at position 1
Loop 2:
str = "-1 Hello world COM-1 speaking"
- first occurrence of COM is at position 16 in this new string
Since you are removing the first three characters of the string when you call substr at the beginning of the second loop, you're looking for the position of "COM" in a slightly different string the second time around, hence the confusion.
If you want to find the position in the original string, you'd want something like
CREATE OR REPLACE PROCEDURE findOccurrence( string IN varchar2, search IN varchar2, offset IN number)
AS
  currentPosition NUMBER;
BEGIN
  currentPosition := INSTR( string, search );
  IF( currentPosition > 0 )
  THEN
    dbms_output.put_line( 'Search string found at position ==> ' || to_char(currentPosition+offset));
    findOccurrence( substr( string, currentPosition+length(search) ),
                    search,
                    currentPosition+length(search)+offset-1 );
  END IF;
END;
scott@jcave > exec findOccurrence( 'COM COM COM', 'COM', 0 );
Search string found at position ==> 1
Search string found at position ==> 5
Search string found at position ==> 9
PL/SQL procedure successfully completed.Justin
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