Conditional compilation

User interface > Translation > Preprocessing > Conditional compilation

Delphi2Cpp uses a preprocessor (pre-translator), which prepares the source text so that directives for the conditional compilation are evaluated and removed.

However, unlike in Delphi conditional compilation, the Delphi2Cpp pre-processor only can evaluate  conditional symbols, but usually cannot evaluate constants in the Delphi language and such constants never can be set by conditional compilation.

For example, conditional expressions like

{$IF CompilerVersion >= 17.0}

are evaluated, but integer values are evaluated and only operators, which also exist in C++. Sizeof-expressions like tho following are evaluated too

{$IF SizeOf(Extended) >= 10} 

  {$DEFINE EXTENDEDHAS10BYTES}

{$ENDIF}

as long, as the size can be taken from the type-map. In System pas the is the following code:

  {$IF SizeOf(Extended) <> SizeOf(TExtended80Rec)}

    {$MESSAGE ERROR 'TExtended80Rec has incorrect size'}

  {$ENDIF }

"TExtended80Rec" is not defined in the type-map and therefore Delphi2Cpp cannot evaluate the expression.

If there is an expression, which cannot be evaluated, a warning is written into the code:

// pre-processor can't evaluate ...

The source code has to be corrected by hand then.

The Delphi2Cpp pre-processor cannot set new Delphi constants as in the following code from the Jedi components in JvConsts.pas

  const

  ...

  {$IFDEF DELPHI26}

  SDelphiKey = 'Software\Embarcadero\BDS\20.0';

  {$ENDIF DELPHI26}

  {$IF not declared(SDelphiKey)}

    {$MESSAGE FATAL 'Declaration for SDelphiKey is missing'}

  {$IFEND}

Even if DELPHI26 is set, SDelphiKey would not be declared

Include directives are executed correctly.

{$I filename}

{$INCLUDE filename}

The file filename is included into the source.

The definitions can be set in the options dialog.

This page belongs to the Delphi2Cpp Documentation