如何在delphi中传递一个字符串数组参数

Question

I have a problem with Delphi.

I wrote a function like this:

function MyFunction(arr: array of AnsiString): Boolean;
begin
  //code here
end;

And now, when I pass an array of AnsiString directly into function, like this, everything works perfectly:

MyFunction(['one', 'two', 'three']);

But, when I try to store this array like this:

var arr: array of AnsiString;

procedure MyProcedure;
begin
  arr[0] := ['one', 'two', 'three'];
  MyFunction(arr[0]);
end;

There is a mismatch error.

I'm a beginner with Delphi, but this is really confusing.

Answer 1

Your second example is not functionally identical to the fist example.

The first example is fine. The function takes an open array as an input parameter, and you are constructing a fixed array of strings directly in that parameter, which is perfectly fine. Any array type can be passed to an open array parameter.

In the second example, you are declaring a dynamic array of strings, but you are not allocating any memory for the array, and you are trying to assign its first element (which is a single string) to point at a fixed array of strings. And then you are trying to pass that element (again, a single string) where an array is expected. That is why the code fails to compile.

The correct way to write your procedure would like more like this:

procedure MyProcedure;
var
  arr: array of AnsiString;
begin
  SetLength(arr, 3);
  arr[0] := 'one';
  arr[1] := 'two';
  arr[2] := 'three';
  MyFunction(arr);
end;

Alternatively:

procedure MyProcedure;
var
  arr: array of AnsiString;
begin
  arr := ['one', 'two', 'three'];
  MyFunction(arr);
end;

Alternatively:

type
  TAnsiStringArray = array of AnsiString;

procedure MyProcedure;
var
  arr: TAnsiStringArray;
begin
  arr := TAnsiStringArray.Create('one', 'two', 'three');
  MyFunction(arr);
end;