CODEWITHSUNDEEP
delphisplitcopymemory
nemoest
nemoest

Reputation: 81

Delphi Split a string with CopyMemory in part-strings using an offset

I want to split a string in X partstrings.

This is my code so far:

procedure SplitFile(var a: StringArray; len: integer; fileString: AnsiString; numberParts: integer);
var
  i, Rest, partSize: integer;
  tmp: AnsiString;
begin
  Rest := len mod numberParts;
  SetLength(a, numberParts);
  partSize := (len - Rest) div numberParts;
  numberParts := numberParts - 1;
  for i := 0 to numberParts do
  begin
    // Get access violation here
    CopyMemory(@a[i][1], @filestring[i * partSize], partSize);
  end;
  if Rest <> 0 then
    CopyMemory(@a[numberParts][numberParts*partSize], @filestring[numberParts*partSize], Rest);
end;

I get an access violation on this line:

CopyMemory(@a[i][1], @filestring[i * partSize], partSize);

I am not sure where exactly the error gets caused. How do I get the Address of a[i], sin't it @a[i][1]? and causes it an error anyway when it tries to access @filestring[i* partSize] in the first loop, cause it would be 0?

I hope someone can explain me that.

Thanks

Upvotes: 0

Views: 647

Answers (2)

Remy Lebeau
Remy Lebeau

Reputation: 597885

Your code is over-complicated for what you are attempting. Try this simpler code instead:

// assuming StringArray is "array of (Ansi)String"...
procedure SplitFile(var a: StringArray; len: integer; fileString: AnsiString; numberParts: integer);
var
  i, partSize: integer;
begin
  partSize := len div numberParts;
  SetLength(a, numberParts);
  for i := 0 to numberParts-1 do begin
    a[i] := Copy(filestring, (i * partSize)+1, partSize);
  end;
end;

On the last iteration, Copy() will truncate the returned substring for you if the requested count is more than the available number of characters at the requested offset.

Upvotes: 2

MBo
MBo

Reputation: 80287

I see three main issues:

  • Overtangled part counting leads to error in array length determination.
  • You have to add 1 to properly address ansistring chars:

  • Must set length of destination strings

    for i := 0 to numberParts {probably - 1} do begin SetLength(a[i], partSize); CopyMemory(@a[i][1], @filestring[i * partSize + 1], partSize); end;

Th same is true for the last piece treatment

Upvotes: 1

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