How to extend structures at runtime

Question

hello,
is there any chance to
extend a data structure at runtime?
normally you define a structure with
data: begin of x,
      field1 type c,
      field2 type n.
data: end of x.
this structure is the basis for your internal tables etc.
it would be definitely nice to add a third field at runtime if it is needed.
in other programming languages it would also be possible to add elements to an array. the question ist: how can i add fields to the structure dynamically?
it could be useful for a lot of situations.
dynamically generated fieldcatalogue for example.
i think i could succeed in changing the structure by using field symbols in combination with dynamically creating data objects by the "CREATE DATA" statement.
has anyone already done something similar?

Answer 1

Hello Gideon,
It is possible using ABAP runtime program generation like in code below.
This program generate a dinamic ALV with N fields. There is a parameter where the user type how many fields he wants to display (or generate).
Then form f_create_dynamic_table generate an internal table with N fields according to the number in the parameter.
You can change the program to generate a dinamic structure if you want, in fact it already does it.
Just cut and paste the program and execute in your system.
Regards,
Mauricio
REPORT zasmm008.
$$ Declarações -
TYPE-POOLS:
  kkblo.    "Tipos para lista especial
FIELD-SYMBOLS:
   TYPE table.
PARAMETERS p_qtd TYPE i OBLIGATORY DEFAULT 10.
$$ Eventos -
INITIALIZATION.
  %_p_qtd_%_app_%-text = 'Dinamic fields quantity'.
START-OF-SELECTION.
  CHECK p_qtd > 0 AND p_qtd < 100.
  PERFORM f_create_dynamic_table.
  PERFORM f_fill_dynamic_table.
  PERFORM f_create_alv.
$$ Forms -
*&      Form  f_create_dynamic_table
FORM f_create_dynamic_table.
  DATA:
    lv_line           TYPE i,
    lv_word(72)       TYPE c,
    lv_form(30)       TYPE c VALUE 'TABLE_CREATE',
    lv_message(240)   TYPE c,
    lp_table          TYPE REF TO data,
    lp_struc          TYPE REF TO data,
    lv_name           LIKE sy-repid,
    lv_cont(02)       TYPE n,
    lv_lng            TYPE i,
    lv_typesrting(6)  TYPE c.
The dynamic internal table stucture
  DATA: BEGIN OF lt_struct OCCURS 0,
          fildname(8) TYPE c,
          abptype TYPE c,
          length TYPE i,
        END OF lt_struct.
The dynamic program source table
  DATA: BEGIN OF lt_inctabl OCCURS 0,
          line(72),
        END OF lt_inctabl.
Sample dynamic internal table stucture
  DO p_qtd TIMES.
    ADD 1 TO lv_cont.
    CONCATENATE 'FIELD' lv_cont INTO lt_struct-fildname.
    lt_struct-abptype = 'C'.
    lt_struct-length = '4'.
    APPEND lt_struct.
  ENDDO.
Create the dynamic internal table definition in the dyn. program
  lt_inctabl-line = 'PROGRAM ZDYNPRO.'.
  APPEND lt_inctabl.
  lt_inctabl-line = 'FORM TABLE_CREATE CHANGING P_TABLE P_STRUC.'.
  APPEND lt_inctabl.
  lt_inctabl-line = 'DATA: BEGIN OF DYNTAB OCCURS 0,'.
  APPEND lt_inctabl.
  LOOP AT lt_struct.
    lt_inctabl-line = lt_struct-fildname.
    lv_lng = strlen( lt_struct-fildname ).
    IF NOT lt_struct-length IS INITIAL .
      lv_typesrting(1) = '('.
      lv_typesrting+1 = lt_struct-length.
      lv_typesrting+5 = ')'.
      CONDENSE lv_typesrting NO-GAPS.
      lt_inctabl-line+lv_lng = lv_typesrting.
    ENDIF.
    lt_inctabl-line+15 = 'TYPE'.
    lt_inctabl-line+21 = lt_struct-abptype.
    lt_inctabl-line+22 = ','.
    APPEND lt_inctabl.
  ENDLOOP.
  lt_inctabl-line = 'END OF DYNTAB.'.
  APPEND lt_inctabl.
  lt_inctabl-line = 'DATA: POINTER TYPE REF TO DATA.'.
  APPEND lt_inctabl.
  lt_inctabl-line = 'CREATE DATA POINTER LIKE DYNTAB[].'.
  APPEND lt_inctabl.
  lt_inctabl-line = 'P_TABLE = POINTER.'.
  APPEND lt_inctabl.
  lt_inctabl-line = 'CREATE DATA POINTER LIKE LINE OF DYNTAB.'.
  APPEND lt_inctabl.
  lt_inctabl-line = 'P_STRUC = POINTER.'.
  APPEND lt_inctabl.
  lt_inctabl-line = 'ENDFORM.'.
  APPEND lt_inctabl.
  CATCH SYSTEM-EXCEPTIONS generate_subpool_dir_full = 9.
    GENERATE SUBROUTINE POOL lt_inctabl[] NAME lv_name
             MESSAGE lv_message LINE lv_line WORD lv_word.
  ENDCATCH.
  PERFORM (lv_form) IN PROGRAM (lv_name) CHANGING lp_table lp_struc.
Dynamic table in <tb> and its header line in <st>
  ASSIGN lp_table->*  TO .
ENDFORM.                    " f_create_dynamic_table
*&      Form  f_create_alv
FORM f_create_alv.
  DATA:
    ls_layout    TYPE slis_layout_alv,
    lv_cont(02)  TYPE n,
    lt_fieldcat  TYPE slis_t_fieldcat_alv WITH HEADER LINE.
  DO p_qtd TIMES.
    CLEAR lt_fieldcat.
    ADD 1 TO lv_cont.
    CONCATENATE 'FIELD' lv_cont INTO lt_fieldcat-fieldname.
    CONCATENATE 'Campo' lv_cont INTO lt_fieldcat-seltext_s
                SEPARATED BY space.
    lt_fieldcat-seltext_m = lt_fieldcat-seltext_s.
    lt_fieldcat-seltext_l = lt_fieldcat-seltext_s.
    lt_fieldcat-outputlen = 10.
    APPEND lt_fieldcat.
  ENDDO.
  ls_layout-zebra = 'X'.
  CALL FUNCTION 'REUSE_ALV_GRID_DISPLAY'
       EXPORTING
            is_layout     = ls_layout
            it_fieldcat   = lt_fieldcat[]
       TABLES
            t_outtab      =
       EXCEPTIONS
            program_error = 1
            OTHERS        = 2.
ENDFORM.                    " f_create_alv
*&      Form  f_fill_dynamic_table
FORM f_fill_dynamic_table.
  DATA:
    lv_line(2)   TYPE n,
    lv_field(2)  TYPE n.
  DO 20 TIMES.
    ADD 1 TO lv_line.
    CLEAR lv_field.
    DO p_qtd TIMES.
      ADD 1 TO lv_field.
      ASSIGN COMPONENT lv_field OF STRUCTURE .
  ENDDO.
ENDFORM.                    " f_fill_dynamic_table