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# Externals Options

In most cases this is not needed but for some C/C++ externals and in some .NET projects it is necessary to specify additional includes, objects or resources.

If you use a library, externals of this library are automatically included. E.g. if you use vision2 the externals for vision2 don't need to be added to the project itself.

- Include: This is where you can enter the location of the directories where the C/C++ compiler will look for the header files that are required. The header files which the C/C++ compiler will look for are the ones that appear in an encapsulation of a C/C++ external in an Eiffel class. Click here to have more information about C/C++ externals specification.
- Object: additional C/C++ object files
- Library: like object files, but will be added last, needed for some very strict C compilers
- Makefile: additional makefiles, if possible use tasks instead

- Resource: .NET resources

  - The .resx resource file format is a XML based format to include objects (such as images and other binary formats) and strings.
  - The .txt resource file format can only contains strings.

Externals have three properties:

- Location: location of the external, will be copied verbatim into the makefile
- Description: an optional description about the external
- Condition: allows the same configuration with externals to work in different situations (e.g. windows and unix) (see conditions)