Delphi – How to define version “and up” ifdefs in Delphi

conditional-compilationdelphi

I was working on getting Log4D working in Delphi XE4, and was getting some compile errors because it couldn't find Contnrs in the uses clause, unless I moved it outside the ifdef it was defined in.

{$IFDEF DELPHI5_UP}
  Contnrs,
{$ENDIF}

A little bit of investigating uncovered that the ifdef is defined in an included file Defines.inc which has a block for each "supported" version of delphi which stops a few versions back:

eg:

{$IFDEF VER170}  { Delphi 2005 }
{$DEFINE DELPHI9}
{$DEFINE DELPHI4_UP}
{$DEFINE DELPHI5_UP}
{$DEFINE DELPHI6_UP}
{$DEFINE DELPHI7_UP}
{$ENDIF}

{$IFDEF VER180}  { Delphi 2006 }
{$DEFINE DELPHI10}
{$DEFINE DELPHI4_UP}
{$DEFINE DELPHI5_UP}
{$DEFINE DELPHI6_UP}
{$DEFINE DELPHI7_UP}

So while it would be easy enough to go ahead and copy and paste the ifdef for Delphi 2006 and create a Delphi XE4 block… this seems like an inelegant solution. It's definitely not future proof…every new version you have to go update this file now so some code that wasn't present in Delphi 4 doesn't make someone else's 15+ year old legacy code explode.

So I was wondering if there's a better way to do conditional compilation such that it really does just check whether you have "Delphi 5 or above" when compiling that line, rather than this format that requires updating every single new version of delphi that comes out.

Best Answer

IIRC, Delphi 6 introduced conditional expressions, which are actually what TLama suggested. To make your code work with Delphi versions below that, you have to check for {$IFDEF CONDITIONALEXPRESSIONS }. If this is not defined, you have to use the old VERxxx scheme to distinguish between the Delphi versions.

For Delphi 6 and higher you can use the built-in constants CompilerVersion and RTLVersion. Which of these you use depends on your code. Whenever you use a new compiler feature test for CompilerVersion. For anything related to the RTL or VCL test for RTLVersion.

It is always a good idea to code against the newest compiler and only use the conditional part for compatibility to older versions. So instead of writing {$IF CompilerVersion >= 26.0} write your code in a way that {$IF CompilerVersion < 26.0} is used. Thus in the future it is much easier to drop support for older compiler versions.

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