Before you can work with a field symbol, you must assign a data object to it. If you attach a structure to a field symbol, you assign a data object to it in the declaration. Untyped field symbols point to the built in data object space once the program starts. space has type c and length 1. Typed field symbols do not point to any field before a data object is assigned to them.
During a program, you can assign data objects to field symbols at any time. You can also assign a series of different data objects to the same field symbol during a program.
To assign a data object to a field symbol, use the ASSIGNstatement. The ASSIGN statement has several variants and parameters.
You can assign single lines from internal tables to field symbols.
You can start a screen sequence from an ABAP program using
which allows you to specify explicitly that a field symbol <fs> should not have a data object assigned to it. If you try to use an unassigned field symbol, a runtime error occurs. There is a special logical expression that you can use to check whether a data object is assigned to a field symbol.