Test268 Section 4

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Section 4 - Advanced RPG techniques (25%)

Use Data Structure arrays

If MyDS is a data structure array of 10 elements, then MyDS(5) will access the fifth element of that data structure array. But how do you access the subfields? That requires a bit more discussion.

When you define a data structure array, you not only use the Dim keyword, but you must also specify the Qualified keyword. The Qualified keyword was introduced in V5R1, and it allows you to specify the name of a data structure subfield qualified by the name of the data structure. For example, if data structure MyDS is defined with the Qualified keyword and it contains a subfield named Subfield1, then you would use the following notation to access the subfield:

MyDS.Subfield1

If data structure MyDS is also defined with the Dim keyword, then something like the following notation is used to access subfields in a specific element:

MyDS(5).Subfield1

In this example, you would be accessing the subfield named Subfield1 in the fifth element in the data structure array MyDS.

Code complex D-specs (e.g., OVERLAY, coding fields without attributes, etc.)

D DataStruct1     DS                  QUALIFIED
D  Field1                       15A   INZ('12345ABCDE12345')
D   Field2                       5A   OVERLAY(Field1)
D   Field3                       5A   OVERLAY(Field1:*NEXT)
D   Field4                       5A   OVERLAY(Field1:*NEXT)
D   Field5                       7A   OVERLAY(Field3:3)

D DataStruct2     DS                  LIKEDS(DataStruct1) INZ(*LIKEDS)

D  Name           S             20
D  Long_name      S             +5    LIKE(Name)
D  Lda_fld        S                   LIKE(Name) DTAARA(*LDA)

Code subprocedures

• Internal Program Sub-Procedure

D Inter_Func      PR            10I 0              
D  Term1                         5I 0 VALUE
D  Term2                         5I 0 VALUE
D  Term3                         5I 0 VALUE

• External Module Sub-Procedure

D Extrn_Func      PR            10I 0 EXTPROC('MODULE_FUCT')             
D  Term1                         5I 0 VALUE
D  Term2                         5I 0 VALUE
D  Term3                         5I 0 VALUE

• External Program Sub-Procedure

D Pgm_Func        PR            10I 0 EXTPGM('PGM_FUCT')             
D  Term1                         5I 0 VALUE
D  Term2                         5I 0 VALUE
D  Term3                         5I 0 VALUE

Declare and use subprocedures

Declare the Function and call it

D Function        PR            10I 0              
D  Term1                         5I 0 VALUE
D  Term2                         5I 0 VALUE
D  Term3                         5I 0 VALUE
D  RC             S             10I 0 INZ(*ZEROS)
 /free
   RC = Function(Term1:Term2:Term3);
   *INLR = *ON;
   RETURN;
 /end-free

start the function and return the results

P Function        B                             
D Function        PI            10I 0              
D  Term1                         5I 0 VALUE
D  Term2                         5I 0 VALUE
D  Term3                         5I 0 VALUE
D Result          S             10I 0                 
 /free
   Result = Term1 ** 2 * 17 + Term2 * 7 + Term3;
   return Result;
 /end-free
P Function        E

Write logic (including I/O operations) without numbered indicators

/Free
 SETLL (variable1:variable2) filename;
 IF %EQUAL(filename);
    READE(N) (variable1:variable2) filename;
    DOW NOT %EOF(filename);
       // logic
       READE(N) (variable1:variable2) filename;
    ENDDO;
 ENDIF; 
/End-Free

/Free
 CHAIN (variable3) filename;
 IF %FOUND(filename);
    // logic
    UPDATE filerec;
 ENDIF;
/End-Free

Code and use /Free format Calc specifications

/Free
 // Convert from a char to Num
 num = %DEC(char);
 // Chain to the correct record, checking for error with no rec lock
 CHAIN(EN) (char) filename1;
 IF %FOUND(filename1) and NOT %ERROR;  // If Condiditon
    CHAIN (num) filename2; // Chain to next file
    IF %FOUND(filename2); // If Condition
       filevar1 += 1;
       filevar2 = char;
       filevar3 = proc_call(filevar1:filevar2); // Call a Procedure
       // Update only field filevar3 in filename2
       UPDATE filerec2 %FIELDS(filevar3); 
    ENDIF;
 ELSEIF %ERROR;
    DSPLY 'There was an error';
    *INLR = %ERROR;
    RETURN;
 ENDIF;
 *INLR = *ON;
 RETURN;
/End-Free

Code and use Short Form expressions (e.g., + =)

i += 1;

Determine appropriate use for prototype keywords, such as CONST, VALUE, and OPTIONS (*NOPASS, *OMIT, *VARSIZE)

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