I read an article about Dynamically Sized Arrays on ITJungle and was wondering if this is not an "making easy thing much more complex" thing.
So as I understand if I define an static variable, including arrays, the runtime reserves the needed space at RUNTIME. So when defining a array of CHAR(10) DIM(10) the whole space would be reserved when starting the program.
So as the article says if I want to have a dynamically increasing array which resizes itself to fit the data like an List<String> in C#, I have to create a CHAR(10) DIM(10). I then have to re-allocate new space only if needed?
Why? The space is already reserved. What reason would someone have to base a array with (lets say) 100 bytes size on a pointer when only needing i.e. 80 bytes?
Am I just missing something? Is the "init-value" for sizing the array just to calm down the compiler so I don't get an error that the "compiler doesn't know the size at compile time"?
For normal arrays, you are correct that the space gets allocated at runtime as soon as the particular arrays scope is reached (start of the program for globals, start of subprocedure for subprocedures).
However, you will notice that the data structure is declared with based(pInfo). based is the keyword that will cause the memory to NOT be allocated. It will instead assume the all the memory for the data structure (included the array member) is already allocated at the location specified by the pointer passed to the based keyword (pInfo in this case).
Effectively, once you use the based keyword you are simply telling the compiler how you would like the memory at the specified pointer to be used but it is up to you to actually manage that memory.
In summary, if I understand your question properly, the statement you made about "knowing the size at compile time" is correct. RPG does not support pointer/array duality or array-like objects like some languages so you essentially just have to declare to RPG that you will NEVER go beyond "init-value" bounds.