what is the differences between +n and (n) in bit operations?

I've found two parameters defined like these:

&TM_PERIOD+4&/&TM_PERIOD(4)&

It's to pass data from a database to a form.

If the format of the data would be DDMMYYYY what开发者_Go百科 are differences between those two parameters?

if TM_PRIOD is in form of DDMMYYYY then

TM_PERIOD(4) equals DDMM
TM_PERIOD+4 equals YYYY

the (4) means 4 characters the +4 means after the 4th character

TM_PERIOD+1(2) = DM
(2 characters after the first)

These are not bit operations. +n specifies a string offset and (n) specifies the length.

They can be used independently of each other as well, so you can use just +n or just (n).

So:

data: lv_text(20) type c.
lv_text = "Hello".
write: / lv_text+2(3).

would output 'llo', for example.