Predefined Data Objects
At runtime, the following data objects are always present, and do not have to be declared:
Constant 'space'
The data object space is a constant with type c. It is one byte long, and contains a space character. As a constant, space cannot be changed.
Self-reference 'me'
A self-reference is an object reference variable called me that is available as a predefined local object in all instance methods and shows the instance in which the method is being executed. The reference type of me is the class in which the instance method is implemented.
Structure 'screen'
You can access the data object screen during screen processing in dialog modules. screen is a structure whose components correspond to the attributes of a screen element.
System Fields in Structure SY
sy is a structure with the ABAP Dictionary data type SYST. The components of sy are known as system fields. System fields contain values that provide information about the current state of the system. They are automatically filled and updated by the ABAP runtime environment. Examples of system fields:
- sy-subrc Return code for ABAP statements(zero if a statement is executed successfully)
- sy-uname User name
- sy-repid Current ABAP program
- sy-tcode Current transaction
- sy-index Number of the current loop pass
System fields are variables and can be changed by the program. However, you should only do so where the system documentation recommends it for a specific field (for example, you can change the value of sy-lsind to navigate between detail lists). In all other cases, you should treat system fields as though they were constants, and only read them. If you change their values, important information for the flow of the program may be lost.
For a complete list of all system fields with notes on their use, refer to