Strange: blank in string. Anybody can explain this?

Question

Hello!
Look at this. Until now I thougt, I had understood ABAP...
Output of the following programm:
1) Strange
2) Strange
3) Strange
4) Strange
5) Strange
6) Strange
Very strange, isn't it?
ABAPDOCU tells, that strings pay attention to blanks.
Can anybody explain this?
REPORT zstrange.
DATA: stringwithspace TYPE string VALUE 'A B',
      teststring TYPE string,
      blankstring TYPE string VALUE ' ',
      l type i.
START-OF-SELECTION.
  IF stringwithspace+1(1) = ' '.
    WRITE: / '1) My guess'.
  ELSE.
    WRITE: / '1) Strange'.
  ENDIF.
  IF stringwithspace+1(1) = blankstring.
    WRITE: / '2) guess'.
  ELSE.
    WRITE: / '2) Strange'.
  ENDIF.
  IF stringwithspace+1(1) = ''.
    WRITE: / '3) guess'.
  ELSE.
    WRITE: / '3) Strange'.
  ENDIF.
  teststring = stringwithspace+1(1).
  IF teststring = ' '.
    WRITE: / '4) Guess'.
  ELSE.
    WRITE: / '4) Strange'.
  ENDIF.
  IF teststring = blankstring.
    WRITE: / '5) Guess'.
  ELSE.
    WRITE: / '5) Strange'.
  ENDIF.
  IF teststring = ''.
    WRITE: / '6) guess'.
  ELSE.
    WRITE: / '6) Strange'.
  ENDIF.

Answer 1

No, thats not strange.
c variables have always a fixed length, it can not contain "nothing". If there are only spaces in, the c variable is treated as empty/initial.
Strings can contain nothing, and they can contain spaces. A string containing blanks is not interpreted as empty/initial.
      blankstring TYPE string VALUE ' ',
What you are doing here is assigning an empty string to the string var blankstring, it does NOT contain a blank.
Constants encapsulated with apostrophes are treated as c variables. But: constants encapsulated within back quotes will be interpreted as string. Change your code to
      blankstring TYPE string VALUE ` `,
Take care of that i used back quotes now, not apostrophes, Now the var blankstring contains a blank and the result in that case will change to MY guess.
Similar the camparison
  IF stringwithspace+1(1) = ' '.
This is comparing a blank with an empty char and thats why you are getting strange.
Change this to
  IF stringwithspace+1(1) = ` `.
and you will get My guess cause now you are comparing a blank with a blank and not a blank with an empty string.
Hope its now clear.