Delphi Initialize Record
Is it safe to use Default() assignment to initialize record variables in Delphi? Tag: delphi Assigning Default(TMyRecord) to a variable of TMyRecord is said to internally call first Finalize and then zero out the memory like FillChar would. Nov 7, 2018 - Custom Managed Records Coming in Delphi 10.3. Code to be executed when records are first initialized, disposed from memory and copied. The Record keyword is one of the most useful, and distinguishing features of Delphi (and the Pascal language). It provides a means of collecting together a set. The Initialize procedure is usually the best way to do this, but it does not initialize any other elements of the array or record. Instead, you can call FillChar to fill the new memory with all zeros, which is a correct initial value for strings, dynamic arrays, interfaces, and Variant s.
Peter Below wrote: > procedure FillArrayOfItems(var A: TarrayOfItems; const aDefault: > TArrayItem); > var > I: integer; > begin > for I:= Low(TAliasArray) to High(TAliasArray) do > PAliasArray(@A)^[I]:= aDefault; > end; Thank you, Peter. I must say, a very interesting approach. Took me quite a bit of time to get around it:) I tried your suggestion and timed it using QueryPerformance stuff. This is the time it took: 0.106033 Then, I lifted your idea of using 'aDefault' and the for-loop version came to 0.404132 IOW, flattening did actually increase the time it took by 24%.
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Perhaps there's another way:) Cheers, Adem. You may try this approach. It needs 15ms on my system. Var Array1: Array [0.66, 0.66, 0.30, 0.24] of record Value1: Integer; Value2: Integer; Value3: Boolean; end; procedure InitArray; var I: Integer; begin with Array1[0, 0, 0, 0] do begin Value1:= MaxInt; Value2:= -MaxInt; Value3:= False; end; for I:= 1 to 24 do Array1[0, 0, 0, I]:= Array1[0, 0, 0, 0]; for I:= 1 to 30 do Array1[0, 0, I]:= Array1[0, 0, 0]; for I:= 1 to 66 do Array1[0, I]:= Array1[0, 0]; for I:= 1 to 66 do Array1[I]:= Array1[0]; end; -- Uwe Raabe Delphi Community Evangelist Uwe's Blog: The Art of Delphi Programming. Quentin Correll wrote: > > Your suggestion is more or less Remy's this alternative. Unless the > > keyword 'absolute' does something magical:) it is not faster. > > You might try it.
Absolute DOES do 'something magical.' Q, It really doesn't.
Here is a brief description: 'absolute' allows you to direct the compiler to treat one or more variables as existing at the same memory location, effectively overlaying one (or more) on top of another. IOW, it is a pointer type casting; except that 'absolute' does it in the compile-time. But, it's got it's own limitations.
> My solution only uses one iteration loop control and one, not three, > assignments! > > I would be interested in seeing your actual results comparisons. I did try to implement it. But, the thing is, I have 3 of those array (with different limits in different dimensions).
And, they are used in a few procedures/functions of the unit. I could declare those arrays in the calling routine and pass them on to the calle as parameters. This would make my code look more elegant too.
Except that I can't. I know it because I did try. Delphi complains about stack size. And, I don't want to double/triple the stack size just to be able to pass these arrays as parameteres. It would only serve the purpose of using 'absolute' in one of the called routines. So, the question, then, boils down to this: Do you know of a way of declaring a local variable that has 'absolute' to a variable defined in the private section of the class?
Cheers, Adem. Adem Meda wrote: Q, Even though this might seem kind of replying to my self, it isn't. This discussion made me review the parts that used pre-dimensioned (static) array idea. > But, the thing is, I have 3 of those array (with different limits in > different dimensions).
Delphi Initialize Records
And, they are used in a few > procedures/functions of the unit. > > I could declare those arrays in the calling routine and pass them on > to the calle as parameters.
This would make my code look more elegant > too. Does walmart allow dogs. > > Except that I can't. I know it because I did try.
> > Delphi complains about stack size. I couldn't pass them as parameters becuase they were large static arrays that made stack unhappy. So, I turned them into dynamic arrays and declared them in the calling routine; passing them to where they are needed. Even though I need to dynamically dimension them [SetLength()], it turns out I don't get any speed drawback as I set them to default in the same loops. What it does save me is this: My app does not any more start off as 100 MB load on RAM.
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Delphi Initialise Record
If you switch to dynamic arrays as you mentioned in another post, you won't be able to use this technique, since each assignment will only be providing a reference to another dynamic array, rather than copying the data. Since dynamic arrays aren't copy-on-write like strings, changing one element in the array will appear to cause other elements to change at the same time. If you don't need the array data for a while after initializing, and the clear takes quite a while (causing program to freeze up for a while), you could clear for 'free' in a thread. Daniel Bartlett wrote: > If you switch to dynamic arrays as you mentioned in another post, you > won't be able to use this technique, since each assignment will only > be providing a reference to another dynamic array, rather than > copying the data. Since dynamic arrays aren't copy-on-write like > strings, changing one element in the array will appear to cause other > elements to change at the same time. All true:) I had to go back to good old loop-through-each-array-for-each-cell; but the stuff we discussed here helped a lot. Such that, dimensioning and initializing of the arrays take almost exactly the same as it took just to initialize the static arrays.