dynamic multidimensional array

Today I got a task to convert as C# desktop application into a Delphi XE application. One thing I learned is about dynamic multidimensional array. In C#, we can do this by just simply using one-liner “new” command and state the array dimension with it. As in Delphi, this is not the case, since all variables had to be declared far-before used.

Dynamic multidimensional array in Delphi can be declared using iterated “array of” keyword

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var
   myInt: array of array of Integer;

Inside “begin“..”end” of a procedure/function that using the array, we can determine or change the array dimension like this:

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SetLength(myInt, 3, 3);

That command will set myInt into 3×3 dimension array. Apparently, Delphi also allowed you to have a multidimensional array that has different number of column for each row, for example:

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SetLength(myInt, 2);
SetLength(myInt[0], 3);
SetLength(myInt[1], 2);

The first row will made myInt array have 2 rows without specifying how may columns. Second line will set the first row to have 3 columns and third line will set the second row of myInt to have 2 columns.

To check how many row or column a multidimensional array had, you can use “Length” command

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Length(myInt);           //this will return number of rows from a multidimensional array
Length(myInt[0]);        //how many columns does first row of myInt had

Destroying a dynamic multidimensional array can be done by assigning the array to nil

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myInt:=nil;

You can’t use dynamic multidimensional array as procedure/function parameter or result type directly. You’ll get error if you do this:

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function foo(myInt: array of array of Integer): array of array of Integer;
begin
  //do something
end;

Instead of that, you had to define your own variable type and until then you can use it as function parameter or result type.

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interface
 
type
  TMyInt: array of array of Integer;

Using your own variable type in function:

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function foo(myInt: TMyInt): TMyInt;
begin
  //do something
end;

Important Notes: if you work on 2 dimensional array that related to object that had table (such as stringgrid) or image/bitmap coordinate, you had to switch the term “row” and “column” I described above. Delphi use this: table_name[column, row];.

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