Hi Angad,
For infoobjects like 0plant or 0comp_code, you will not find the length or other information on sap help website.
But there is a work around. This will work for most but not for all. You can get the length from the R/3 client of your trial version. You need to find the corresponding field name. Then go to se11 in R/3 client and find our in which table it is used. Or just see the data element. Length and data type can be found there.
E.g. you want the info for field 0comp_code. Go to google search for help.sap.com "0COMP_CODE_ATTR" . You will get results from sap help.
http://help.sap.com/erp2005_ehp_06/helpdata/EN/43/ddf91d21a84772b7f679bc6c9d0f0b/content.htm
From this page you will find that the field name is BUKRS. In R.3 client of ur trial version u can find d rest.
The easiest way will be to search for tables in R/3 and find out.
Regards,
Sujit