Returning arrays

What is translated > Types > Arrays > Returning arrays

In Delphi arrays can be returned from functions by value, but this is not allowed for C-style arrays  in C++. In C++ arrays are passed to functions by reference instead. That's what Delphi2Cpp*) does too. If TObjectArray is defined as:

type TObjectArray = array[1..3] of TObject;

or in C++:

typedef TObject* TObjectArray[3/*# range 1..3*/];

the following Delphi function:

function CreateArray: TObjectArray;

begin

  Result[1] := TObject.Create;

  Result[2] := TObject.Create;

  Result[3] := TObject.Create;

end;

becomes in C++ to:

TObjectArray& CreateArray(TObjectArray& result, uniquetype u)

{

  result[1 - 1] = new TObject();

  result[2 - 1] = new TObject();

  result[3 - 1] = new TObject();

  return result;

}

This function receives the array as reference parameter, so it can return the reference without danger, There is a second uniquetype parameter, which distinguishes the function from a possible overload:

procedure CreateArray(var arr: TObjectArray);

void CreateArray(TObjectArray& arr)

The function call:

procedure Test;

var

  arr2: TObjectArray;

begin

  arr2 := CreateArray;

end;

is translated by Delphi2Cpp to

void Test()

{

  TObjectArray arr2;

  CreateArray(arr2, uniquetype());

}

In this example the returned array reference isn't used at all. It is used however, if CreateArray delivers the value for another function:

procedure ProcessArray(arr: TObjectArray);

procedure Test2;

begin

  ProcessArray(CreateArray);

end;

This becomes in C++:

void Test2()

{

  TObjectArray arrayreturn__0; ProcessArray(CreateArray(arrayreturn__0, uniquetype()));

}

At first Delphi2Cpp creates a local TObjectArray, which is passed to the CreateArray function and finally is directly passed as reference parameter to the other function. The treatment of array properties is similar.

*)  In contrast to Delphi2Cpp the old Delphi2Cpp in such cases created a helping array in the file scope which is used for an intermediate copy of the array

This page belongs to the Delphi2Cpp Documentation