How do include something if no defines are found

Question

I use the following code in my settings classes to determine what to use. But now I have run in to the problem that I had forgotten to copy the correct .INC file to my project folder and that give me an AV since none of the defines are found. How do I make sure that if none of the defines are found then U_SettingsConnIni are always in the uses section

 uses
  Dialogs, Forms, SysUtils,
{$IFDEF SETTINGSINI}
  U_SettingsConnIni,
{$ENDIF}
{$IFDEF SETTINGSREG}
  U_SettingsConnReg,
{$ENDIF}
{$IFDEF SETTINGSXML}
  U_SettingsConnXml,
{$ENDIF}
  U_SectionNames;

If only one define will be specified at a time, use [`IF..ELSE`](http://docwiki.embarcadero.com/RADStudio/XE3/en/IF_directive_(Delphi)). — TLama, Aug 23 '13 at 15:54

score 3 · Answer 1 · answered Aug 23 '13 at 16:33

Just like ordinary if blocks, $ifdef compiler directives support $else. Furthermore, they can be nested.

uses
  Dialogs, Forms, SysUtils,
{$IFDEF SETTINGSREG}
  U_SettingsConnReg,
{$ELSE}
  {$IFDEF SETTINGSXML}
  U_SettingsConnXml,
  {$ELSE}
  U_SettingsConnIni,
  {$ENDIF}
{$ENDIF}
  U_SectionNames;

David Heffernan · Accepted Answer · 2013-08-24T04:53:00.080

3

This is a scenario better suited to the more powerful $IF than the rather limited $IFDEF.

uses
  Dialogs, Forms, SysUtils,
{$IF Defined(SETTINGSREG)}
  U_SettingsConnReg,
{$ELSEIF Defined(SETTINGSXML)}
  U_SettingsConnXml,
{$ELSE}
  U_SettingsConnIni,
{$IFEND}
  U_SectionNames;

In the latest versions of Delphi you can use $ENDIF here rather than $IFEND if you prefer.

If you want to fail if no conditional is defined, you can do this:

uses
  Dialogs, Forms, SysUtils,
{$IF Defined(SETTINGSREG)}
  U_SettingsConnReg,
{$ELSEIF Defined(SETTINGSXML)}
  U_SettingsConnXml,
{$ELSEIF Defined(SETTINGSINI)}
  U_SettingsConnIni,
{$ELSE}
  {$Message Fatal 'Settings file format conditional must be defined'}
{$IFEND}
  U_SectionNames;

edited Aug 24 '13 at 04:53

answered Aug 23 '13 at 19:56

David Heffernan

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Hefferman am I right to assume that your solution eliminates the need for the code by Jan Doggen? – OZ8HP Aug 23 '13 at 21:15
I'll update the answer to show how to force at least one define. – David Heffernan Aug 24 '13 at 04:49

score 0 · Answer 3 · edited Aug 23 '13 at 20:48

0

An alternative method (not exactly answering your question), if you know that one of the defines is required, is to make sure that the compilation fails. In your case that would be:

{$IFNDEF SETTINGSINI}
{$IFNDEF SETTINGSREG}
{$IFNDEF SETTINGSXML}
This line does not compile
{$ENDIF}
{$ENDIF}
{$ENDIF}

That way if none of the conditional defines is set, the compiler will choke on This line does not compile.

edited Aug 23 '13 at 20:48

Remy Lebeau

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answered Aug 23 '13 at 18:34

Jan Doggen

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that should have been my next question - how to check if none of the defines have been set. – OZ8HP Aug 23 '13 at 20:38

How do include something if no defines are found

3 Answers3