Define a new Data Structure from one that is nested

In the past I have written about nesting data structures, a way to contain data structure(s) within another data structure. And there are times I have wanted to define a new data structure to be identical to another using the LIKEDS keyword.

01 dcl-ds One qualified ; 02 OneSF1 char(1) ; 03 dcl-ds Two ; 04 TwoSF char(5) ; 05 end-ds ; 06 OneSF2 char(1) ; 07 end-ds ; 08 dcl-ds Test1DS likeds(One) ;

Lines 1 – 7: I have one data structure, One.

Lines 3 – 5: I have another data structure embedded within it, Two.

Line 8: I have defined this new data structure using the qualified name of the data structure One, and this one will also include Two.

After compiling the program I can look in the source listing and see that Test1DS is the same size as One.

Field Attributes ONE DS(7) ONESF1 A(1) ONESF2 A(1) TWO DS(5) TWOSF A(5) TEST1DS DS(7)

I can even use the nested data structure, Two, in my new data structure:

10 Test1DS.OneSF2 = 'Y' ; 11 Test1DS.Two.TwoSF = '12345' ; Debug: EVAL test1ds TEST1DS.ONESF1 = ' ' TEST1DS.TWO.TWOSF = '12345' TEST1DS.ONESF2 = 'Y'

What if I want to define a data structure like the nested data structure?

09 dcl-ds Test2Ds likeds(One.Two) ;

Previously when I compile the program with line 9 in it I would get the following errors:

09 dcl-ds Test2DS likeds(One.Two) ; ===> a ===> bbbbbbb *RNF0622 20 a 000800 A qualified name is not allowed in this context. *RNF3371 20 b 000800 The parameter ONE.TWO for keyword LIKEDS is not a data structure.

Fortunately the new Technology Refreshes, IBM i 7.4 TR2 and 7.3 TR8, "fixed" this. When I compiled the program, on a partition with the new TRs, no error occurred and I can see the new data structure is defined as I expected:

Field Attributes ONE DS(7) ONESF1 A(1) ONESF2 A(1) TWO DS(5) TWOSF A(5) TEST2DS DS(5)

Line 12, below, shows I can use the qualified subfield when using the new data structure.

12 Test2DS.TwoSF = '54321' ; Debug: EVAL test2ds TEST2DS.TWOSF = '54321'

 

You can learn more about the changes to RPG's LIKEDS from the IBM website here.

 

This article was written for IBM i 7.4 TR2 and 7.3 TR8.