A field symbol is something akin to a pointer in C in that once you have assign it the field symbol then 'becomes' the variable that you assign it to.
As to their use, a good example would be a routine that takes an internal table and translates that table to a CSV file or some such.
That's easy if you specify the table in the subroutine. You can then loop round the table and move the individual fields of the table to a variable and then output them.
But.... what if you want to use the code on another table ? You cannot pass the table as a parameter because the definition of the table parameter in the subroutine is different.
Well. You could copy the subroutine and use the second table definition so that's easy enough and not too disgraceful
But hang on..... I've got another job that requires a download to a CSV file.... Oooops - that's copy 3 of essentially the same subroutine.
Using field symbols, you can do all of the above with one subroutine, and have the added bonus that you do not have to change the subroutine for each table you want to download:
Code:
Form Out_Local Tables t_outtable
using pu_file like zfilepath-finalpath
pu_sdf type boolean
changing pc_status type status_code.
*
Field-Symbols: <f_field>.
*
Data: t_csv like zraw_csv occurs 0 with header line,
w_csv like zraw_csv,
w_lines type i,
w_charout(2000) type c,
w_ftype(1) type c,
w_len type i,
w_offset type i.
*
* Translate the itab to csv format
*
Loop at t_outtable.
*
* Take this record and change it to a CSV record.
*
Do.
Assign component sy-index
of structure t_outtable to <f_field>.
*
* Last field ?
*
If sy-subrc <> 0.
Exit.
Else.
Write <f_field> to w_charout.
Describe field <f_field> type w_ftype.
Describe field <f_field> length w_len.
If c__numeric cs w_ftype.
Perform Format_Number using w_charout
changing w_charout.
EndIf.
If sy-index = 1.
Move w_charout to t_csv-inline.
Move w_len to w_offset.
Else.
If pu_sdf = False.
Concatenate t_csv-inline ',' w_charout
into t_csv-inline.
Else.
Move w_charout to t_csv-inline+w_offset.
Add w_len to w_offset.
EndIf.
EndIf.
EndIf.
EndDo.
*
* Write the completed line out...
*
Append t_csv.
EndLoop.
Move pu_file to String_filename.
*
* Is this an empty file ?
*
Describe table t_csv lines w_lines.
If w_lines = 0.
Move 'NO DATA FOUND' to t_csv-inline.
Append t_csv.
EndIf.
Call Function 'GUI_DOWNLOAD'
Exporting
Filename = String_Filename
Tables
Data_Tab = T_CSV
Exceptions
File_Write_Error = c_could_not_create_output
No_Batch = c_no_batch
Gui_Refuse_Filetransfer = c_gui_refuse_filetransfer
Invalid_Type = c_invalid_type
Others = c_other_interface_error.
Move sy-subrc to pc_status.
EndForm.
Another use for field symbols is where you build a list of variables in a table at run time and then wish to access those variables.
This routine is part of docs.zip from the repository. Docs.zip can be downloaded and contains many routines for reporting, creating BDC's and so on. These are resuable routines that do not require any changes what so ever to be used in different programs. The routines access different variables and values in different ways depending on the program calling them.
This routine refreshes the values of any input parameters that are on your input screen without having to press the return key or actually execute the report. Again, the routine knows nothing about the individual parameters on the screen:
Code:
Form Read_Screen_Values.
*
Field-Symbols <f_fieldname>.
*
Data: Begin of t_dynpread occurs 0.
Include Structure dynpread.
Data: End of t_Dynpread.
*
Zap t_dynpread.
Loop at Screen.
If Screen-Group3 = 'PAR'.
Move Screen-Name to t_dynpread-fieldname.
Append t_dynpread.
EndIf.
EndLoop.
Call Function 'DYNP_VALUES_READ'
Exporting
Dyname = syst-cprog
Dynumb = syst-dynnr
* Request = 'A'
Tables
Dynpfields = t_dynpread
Exceptions
Invalid_Abapworkarea = 0
Invalid_Dynprofield = 0
Invalid_Dynproname = 0
Invalid_Dynpronummer = 0
Invalid_Request = 0
No_Fielddescription = 0
Invalid_Parameter = 0
Undefind_Error = 0
Others = 0.
Loop at t_dynpread.
Assign (t_dynpread-fieldname) to <f_fieldname>.
Move t_dynpread-fieldvalue to <f_fieldname>.
EndLoop.
EndForm.
So, without field symbols, you would have to code this routine for each individual report.
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