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Is there way of copying the whole array into another array? (Other than using a For-loop)

开发者 https://www.devze.com 2023-01-12 12:02 出处:网络
Is there way of copying the whole array into another array? Other than using开发者_如何学运维 a for-loop.

Is there way of copying the whole array into another array? Other than using开发者_如何学运维 a for-loop.

Does the move or copy command work for this? I did try but it had an error: "Incompatible types".

Should I stick to the for-loop?


To be on the safe side, use the Copy function on dynamic arrays, as it handles the managed types internally. The arrays must be of the same type, i.e. declared in the same expression:

var  
    a, b: array of string;

or by defining a custom array type:

type   
    TStringArray = array of string;  
var 
    a: TStringArray;  
//...and somewhere else
var  
    b: TStringArray;  

then you can do:

a := Copy(b, Low(b), Length(b));  //really clean, but unnecessary 
//...or   
a := Copy(b, 0, MaxInt);  //dynamic arrays always have zero low bound 
                          //and Copy copies only "up to" Count items  

You'll have to use a loop on static arrays and when mixing array types (not that I'd recommend doing it).
If you really have to use Move, remember checking for zero-length, as the A[0] constructs can raise range checking errors, (with the notable exception of SizeOf(A[0]), which is handled by compiler magic and never actually executes).
Also never assume that A = A[0] or SizeOf(A) = Length(A) * SizeOf(A[0]), as this is true only for static arrays and it will bite you really badly if you later try to refactor huge codebase to dynamic arrays.


For dynamic arrays:

var A,B: array of Byte;

begin
  SetLength(A, <size>);
  //initialize A

  B:= A; 
  SetLength(B,Length(A));

end;

In dynamic arrays, the assignment statement duplicates only the reference to the array, while SetLength does the job of physically copying/duplicating it, leaving two separate, independent dynamic arrays.


See article on delphibasics.co.uk

You can copy an array using Copy method (pass in 0 for the index and Length(Source) as count to copy the full contents).

Do NOT use Move or CopyMemory for arrays of string/array/interface/etc managed types. Doing so will bypass Delphi's ref-counting mechanics and will result in memory leaks and corrupted data.


1- If your array doesn't contain any string or dynamic array, you can use move, but dynamic arrays are not to be handled like fixed-sized arrays:

var A,B: array[0..10] of integer;
    DA, DB: array of double;
    i: integer;
begin
  for i := low(A) to high(A) do
    A[i] := i;
  move(A[0],B[0],length(A)*sizeof(A[0]));  // first version, compiler does the stuff
  move(A[0],B[0],sizeof(A)); // it works
  move(A[0],B[0],40); // if you know what you're doing, since sizeof(A)=40
  SetLength(DA,10); // DA[0]..DA[9]
  for i := 0 to high(DA) do // or for i := 0 to 9 if you know what you're doing
    DA[i] := 
  SetLength(DB,length(DA)); 
  if length(DA)<=length(DB) then // if your dynamic array may be void, use this before to avoid GPF
    move(DA[0],DB[0],length(DA)*sizeof(DA[0]));
  if pointer(DA)<>nil then // this will just check that DA[] is not void
    move(pointer(DA)^,pointer(DB)^,length(DA)*sizeof(double)); // similar to previous
end;

2- If your array contains strings or other reference content array, you have to use a loop:

var A,B: array[0..10] of string;
    i: integer;
begin
  for i := 0 to high(A) do
    A[i] := IntToStr(i);
  for i := 0 to high(A) do
    B[i] := A[i]; // this doesn't copy the string content, just add a reference count to every A[], and copy a pointer: it's very fast indeed.
end;


You can use a record type that uses a generic function to copy arrays to a dynamic TArray variable, which I have started using:

 TGen = record // Unused record to allow generic functions.
 public
      ...
       class function arrayCopy<T>(const a: array of T): TArray<T>; static;
 end;



class function TGen.arrayCopy<T>(const a: array of T): TArray<T>;
var i: integer;
begin
  SetLength(result, length(a));
  for i := Low(a) to High(a) do
    result[i] := a[i];
end;

Given a form variable

dtls: TArray<TGridSetupDetails>;

and a parameter assigned from an array over an enumerated type

const adtls: array of TGridSetupDetails

you can initialize the form variable:

  dtls := TGen.arrayCopy<TGridSetupDetails>(adtls);
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