Can I use string "IsEmpty" methods in Delphi

Question

Embaracdero documents "IsEmpty" methods for string types, which I've used successfully with C++ Builder code.

WideString s;

if (s.IsEmpty())
   ....

I tried the same from Delphi, and couldn't get it to compile:

var s: WideString;
begin
  if s.IsEmpty then
  ....

I know you can compare with an empty string, or call the Length function, but is it possible to call this IsEmpty method from Delphi?

EDIT: Just to clarify, this wasn't meant as a String vs Widestring issue.

Basically, the docs I link to above describe a Pascal syntax, as well as a C++ one, yet this doesn't seem to work. I assume this is just a flaw in the documentation.

Returns true if the System::WideString::WideString is empty.

Pascal: function IsEmpty: bool;

You may not think it's a WideString vs. string issue, but it is. — Craig Stuntz
– Craig Stuntz, Commented Jun 19, 2009 at 15:11
@Craig - The question shouldn't involve strings, only WideStrings. Can you elaborate? — Roddy
– Roddy, Commented Jun 19, 2009 at 15:13
It involved strings before you edited the question to remove them. — Craig Stuntz
– Craig Stuntz, Commented Jun 19, 2009 at 15:24

idursun · Accepted Answer · 2009-06-19 12:45:46Z

15

String is not a class in Delphi therefore it has no methods, you have to use functions for string manipulations like Length, Copy, etc... String is a class in C++ so maybe you are confused by that.

answered Jun 19, 2009 at 12:45

idursun♦

6,3701 gold badge40 silver badges51 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Roddy Over a year ago

Thanks. That's the heart of it: String types are all classes in C++, but not in Delphi. The Codegear documentation is wrong to list pascal equivalents to these methods.

Oliver Giesen Over a year ago

MY guess is that the Pascal equivalents in the help probably refer to Delphi.NET where Strings are classes... (haven't checked this myself yet)

idursun Over a year ago

Yes, Delphi documentation is all messed up in these versions but at least CodeGear is trying to gather something better via updates.

Toon Krijthe · Accepted Answer · 2009-06-19 13:12:09Z

5

Delphi is an hybrid language. It contains basic types and classes. Only classes (and records and objects) can contain methods.

String is a basic type, although a special one. It's the only type that has a reserved word. That's why its often written with a lowercase (string) unlike other types which have a starting captial (Integer).

You can if you like:

type
  TString = class
  private
    FString: string;
  public
    constructor Create(const AValue: string);

    property &String: string read FString write FString;
    property IsEmpty: Boolean read GetIsEmpty;
    // ...
  end;

edited Jun 19, 2009 at 13:12

answered Jun 19, 2009 at 12:58

Toon Krijthe

53.6k38 gold badges151 silver badges204 bronze badges

1 Comment

Toon Krijthe Over a year ago

You can prefix a reserved word (like string or while) with a & to use it as a normal identifier.

Craig Stuntz · Accepted Answer · 2009-06-19 16:06:46Z

5

No. string is not WideString, even in D2009. You wouldn't want to, either; comparing with nil/empty string is much faster than a method call.

In Delphi:

var 
  s: string;
begin
  if s = '' then begin
    ShowMessage('It is empty or nil.');

...for string detects both nil and empty string (which is = nil).

edited Jun 19, 2009 at 16:06

answered Jun 19, 2009 at 12:46

Craig Stuntz

127k12 gold badges257 silver badges275 bronze badges

4 Comments

Roddy Over a year ago

Okaayyyy. I get this: [DCC Error] Unit69.pas(31): E2010 Incompatible types: 'string' and 'Pointer' What am I doing wrong? (this with D2007, by the way.)

Craig Stuntz Over a year ago

Error in my example. Fixed. The point is that Delphi actually compares with nil under the hood (look at disassembly).

Fabricio Araujo Over a year ago

You can compare (and NEED to compare) strings with nil in Delphi.Net. In native Delphi, it's enough to compare with EmptyStr or '' .

Craig Stuntz Over a year ago

In .NET, use string.IsNullOrEmpty()

Dmitry Belkeivch · Accepted Answer · 2018-12-03 16:47:14Z

2

In the new editions you can use many string helper functions and s.IsEmpty too.

answered Dec 3, 2018 at 16:47

Dmitry Belkeivch

331 silver badge5 bronze badges

1 Comment

Phil B Over a year ago

Should be the top answer these days? In System.SysUtils (D10.4) in regards to EmptyStr it says: "{ Empty string and null string pointer. These constants are provided for backwards compatibility only. }" Plus "foo.IsEmpty" compared to "(foo = EmptyStr)" seems much nicer in my opinion.

SimaWB · Accepted Answer · 2009-06-19 12:39:15Z

1

if Trim(s)='' then

???

answered Jun 19, 2009 at 12:39

SimaWB

9,3042 gold badges44 silver badges48 bronze badges

2 Comments

Roddy Over a year ago

I know there are other ways. I want to know if IsEmpty can actually be used.

curious slab Over a year ago

function IsEmpty(s:string):boolean; begin; result:=length(s)=0; end; Now you can use it ;-)

Collectives™ on Stack Overflow

Can I use string "IsEmpty" methods in Delphi

5 Answers 5

3 Comments

1 Comment

4 Comments

1 Comment

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

3 Comments

1 Comment

4 Comments

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related