
                                 Externals
                                      
   Here is the information you need if you want to call C or Java code
   from Eiffel code (to call Eiffel feature from C or Java see [1]cecil
   file).
   
   The most common way to call external code from Eiffel is to use the
   external feature definition as described in the book "Eiffel The
   Language". See also the SmallEiffel directory lib_show/external to
   have some examples.
   
   Below is the current list of SmallEiffel external specifications.
   
   external "C_WithoutCurrent"
   
   Simple call to a C function (or procedure). The external called
   routine does not get Current as an argument. A C prototype is
   automatically added in a generated C header file. Use this when you
   provide yourself the C code for the external routine.
   Note: for compatibility with other Eiffel compilers external "C" is
   treated exactly as external "C_WithoutCurrent".
   
   external "C_WithCurrent"
   
   C call with Current. The external called routine gets Current as its
   first argument. A C prototype is automatically added in a generated C
   header file. Use this when you provide yourself the C code for the
   external routine.
   
   external "C_InlineWithoutCurrent"
   
   Similar to "C_WithoutCurrent", except that no prototype is produced.
   Use this if you already have the corresponding prototype coming from
   somewhere else (stdio.h for example), which is likely if you call a
   routine from a standard C library (e.g. printf). Actually, the name is
   not really well chosen, since "Inline" has little to do with this...
   
   external "C_InlineWithCurrent"
   
   Similar to "C_WithCurrent", except that no prototype is produced.
   Use this if you already have the corresponding prototype coming from
   somewhere else (stdio.h for example), which is likely if you call a
   routine from a standard C library (e.g. printf). Actually, the name is
   not really well chosen, since "Inline" has little to do with this...
   
   external "SmallEiffel"
   
   This external specification is reserved to the SmallEiffel 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 INTEGER is
   direcly mapped as C '+' by compile_to_c. For the same infix "+",
   command compile_to_jvm produce the appropriate Java virtual machine
   byte code.
   
   external "JVM_invokestatic"
   
   Calling a Java static method. As it is a static Java call, the Eiffel
   receiver is not used. The "alias" field of the feature is used to
   indicate the Java class, the Java function name and the corresponding
   Java bytecode descriptor. Syntax to use in the alias string is :
          alias "<JavaClassPath>.<MethodName> <Descriptor>"
          
   A dot is the separator between <JavaClassPath> and <MethodName>.
   A blank character is the separator between <MethodName> and
   <Descriptor>.
   The <JavaClassPath> uses the JVM internal notation as described in
   JVMS(*). For example, when one wants to use java.lang.Math, the
   <JavaClassPath> is "java/lang/Math". The <MethodName> gives the Java
   method name. The <Descriptor> gives the internal Java bytecode
   descriptor as described in JVMS(*).
(*) - JVMS -
   "The Java Virtual Machine Specification",
   Tim Lindholm and Frank Yellin, The Java Series,
   Addison-Wesley, ISBN 0-201-63452-X.

   external "JVM_invokevirtual"
   
   Calling a Java virtual method. As for "JVM_invokestatic", the alias
   string gives all needed information to call the virtual function. The
   Current Eiffel target is not used (only arguments and the result are
   considered).
   
   Inlining C code
   
   Another way to call C code from Eiffel is to use "c_inline_c" or
   "c_inline_h" as defined in GENERAL. 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
   SmallEiffel produces. For portability, it is also much better to use
   previous solutions.
   People who tinker with the C code generated by SmallEiffel, not
   limiting themselves to the Cecil and/or external interfaces, should
   also read [2]this page about the C code generated by SmallEiffel,
   Otherwise they might get into trouble.
   
                                   [Line]
   Copyright © Dominique COLNET and Suzanne COLLIN - [3]<colnet@loria.fr>
                     Last update: 05 May 1999, by OZ. 

References

   1. file://localhost/home/colnet/SmallEiffel/man/man/cecil.html
   2. file://localhost/home/colnet/SmallEiffel/man/man/c_code.html
   3. mailto:colnet@loria.fr
