Delphi silently cropping string literals

Question

Delphi 2009 Win32.

The code below tries to add a 257 length string to a memo. It compiles and runs fine, but nothing is added to the memo.

Memo1.Lines.Add('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa');

Looks like a compiler bug. Is it? Because if the string was 256 long, I'd get a compiler error and couldn't compile the app.

Any way to make the app break when the developer tries to do something like this?

I know I could split the string and make this code work, but my point is to prevent developers for using this invalid code without noticing.

Thanks

Answer 1

I don't know about D2009, but under Delphi 6 at least, string literals are limited to 255 characters, and the compiler diagnoses the error.

Answer 2

In Delphi 2007, I get:

[DCC Error] Unit1.pas(29): E2056 String literals may have at most 255 elements

In Delphi 5, I get:

[Error] Unit1.pas(29): String literals may have at most 255 elements

If the D2009 behavior is as you describe, then two things come to mind:

1 - They expanded the limit on the # of chars in a string, but the TMemo can still only accept up to 255.

or

2 - It's a plain old bug

As far as preventing it, the only thing I can think of is to make a regex to search for these strings in your .PAS files.

Answer 3

This is a Delphi 2009 bug with string literals, it should raise the same error as D2007.

Try latest version of Andreas IDE Fix pack, its supose to fix this bug. http://andy.jgknet.de/blog/?page_id=246

Answer 4

The string literal can be only 255 characters long. Not sure why they kept this limitation. But you can solve it using multiple literals:

Memo1.Lines.Add('i have 128 chars' + 'i also have 128 chars').

Answer 5

I agree with Gamecat, however if your dealing with a string that large, I would break it into muliple lines to assist in reading/editing.

if you are LITTERALLY trying to create 257 "a"'s then why not use the DupeString function in the StrUtils unit?

Memo.Lines.Add( DupeString('a',257) );

Much easier to read, and maintain later. If you are doing this in a loop and therefore are worried about performance, then assign the function result to a local variable and use the variable.

var
  sLotsOfAs : string;
  ix : integer;
begin
  sLotsOfAs := DupeString('a',257);
  for ix := 0 to 1000000 do
    Memo.Lines.Add( sLotsOfAs );
end;