Here is the information you need if you want to call C code, C++ code as well as Java code from your Eiffel code (to call an Eiffel feature from C, C++ or Java see cecil documentation).

Below is the current list of SmartEiffel external language specifications.

The most common way to call external C code from Eiffel is to use the external "C" feature definition as described in the book "Eiffel The Language". The best is to start to browse examples of the SmartEiffel distribution in directory tutorial/external/C where you'll find external "C", external "C inline", external "C macro" examples.

The most common way to call external C++ code from Eiffel is to use the external C++ feature definition as described in the book "Eiffel The Language". The best is to start to browse examples of the SmartEiffel distribution in directory tutorial/external/C++ where you'll find external "C++" examples.

A brand new interface to call Java method or Java static method is also available. Obviously, this one is only supported when using the compile_to_jvm command (conversely, previous one are only supported when using the compile_to_c command). Again, and especially for this brand new one, the best is to start to browse examples of the SmartEiffel distribution in directory tutorial/external/Java.

This external specification is reserved to the SmartEiffel compiler itself. Do not use it. Such a feature is directly supported both by compile_to_c and compile_to_jvm. For example, infix "+" of class INTEGER is directly mapped as C '+' by compile_to_c and mapped as an iadd JVM bytecode by compile_to_jvm.

Another way to call C code from Eiffel is to use "c_inline_c" or "c_inline_h" as defined in our GENERAL class. The argument of "c_inline_c" (or "c_inline_h") must always be a manifest string which may contains the C code you want to put inlieu.
Using c_inline_[c/h] also implies you do know exactly the C code SmartEiffel produces. For portability, it is also much better to use previous solutions.
People who tinker with the C code generated by SmartEiffel, not limiting themselves to the Cecil and/or external interfaces, should also read this page about the C code generated by SmartEiffel, Otherwise they might get into trouble.