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external.txt
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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