Conditional Compiler Options

From Lazarus wiki

English (en) français (fr)


Since Lazarus 0.9.29 you can define build modes and conditional compiler options. These options depend on current target OS, CPU, widgetset and project's build mode.

For conditionals see here Macros and Conditionals.

You can set the build macros for a package via package editor / Compiler Options / Build Macros.

You can set the build macros for a project via Project / Project Options / Compiler Options / Build Macros.

Target specific units - Doable via FPC directives, no Lazarus extras needed

Concrete situation: LCL extensions package has a unit (OleUtils) that implements TOLEStream. It only makes sense in Windows. Currently the unit is added in all widgetsets but all code is wrapped around a ifdef Windows define so is seen as a dummy unit in other widgetsets.


  • All units should be added to the package, independent if they are used. If a unit should not always be compiled (not added to the uses section of the package), just unset the 'uses unit' checkbox and add for example {$IFDEF win32}uses oleutils{$ENDIF} to a package unit.
  • You can put units and include files specific to targets into sub directories as demonstrated in the Lazarus and FPC sources (units/$(TargetOS)).
  • Since 0.9.31 multiple files with the same name can be added to packages.

+=What will not be implemented==

  • A global Debug/Verbose buildmode. Almost no one wants to increase verbosity of all packages, nor debug all packages. But you can define one for your own packages.
  • Conditional units. This is already flexible doable via FPC directives and IDE macros.

Future development / Wishes

  • Use a package only under one target, e.g. only under Windows and OS X, but not under Linux or BSD.
Directives, definitions and conditionals definitions
global compiler directives • local compiler directives

Conditional Compiler Options • Conditional compilation • Macros and Conditionals • Platform defines