# 15 SWIG and C#

The purpose of the C# module is to offer an automated way of accessing existing C/C++ code from .NET languages. The wrapper code implementation uses the Platform Invoke (PINVOKE) interface to access natively compiled C/C++ code. The PINVOKE interface has been chosen over Microsoft's Managed C++ interface as it is portable to both Microsoft Windows and non-Microsoft platforms. PINVOKE is part of the ECMA/ISO C# specification.

The C# module is one of the more recently added language modules to SWIG and consequently is missing some functionality available in some other SWIG modules. The C# module is very similar to the Java module, so until some documentation has been written, please use the Java documentation as a guide to using SWIG with C#. The rest of this chapter should be read in conjunction with the Java documentation as it lists the main differences.

Director support (virtual method callbacks into C#) has not yet been implemented and is the main missing feature compared to Java. The other missing feature is the lack of typemaps for wrapping STL code as well as a few minor utility typemaps in the various.i library.

Currently enums are wrapped with C# integers. Be warned that this will change in a forthcoming release. C# enums will be generated instead.

The most noteable differences to Java are the following:

- When invoking SWIG use the `-csharp` command line option instead of `-java`.
- C/C++ variables are wrapped with C# properties and not JavaBean style getters and setters.
- Typemap equivalent names:

  >     jni                         -> ctype
  >     jtype                       -> imtype
  >     jstype                      -> cstype
  >     javain                      -> csin
  >     javaout                     -> csout
  >     javainterfaces              -> csinterfaces
  >     javabase                    -> csbase
  >     javaclassmodifiers          -> csclassmodifiers
  >     javacode                    -> cscode
  >     javaimports                 -> csimports
  >     javaptrconstructormodifiers -> csptrconstructormodifiers
  >     javagetcptr                 -> csgetcptr
  >     javafinalize                -> csfinalize
  >     javadestruct                -> csdestruct
  >     javadestruct_derived        -> csdestruct_derived

- Additional typemaps:

  >     csvarin                     C# code property set typemap
  >     csvarout                    C# code property get typemap

- Feature equivalent names:

  >     javaconst                   -> csconst
  >     javamethodmodifiers         -> csmethodmodifiers

- Pragma equivalent names:

  >     pragma(java)                -> pragma(csharp)
  >     jniclassbase                -> imclassbase
  >     jniclassclassmodifiers      -> imclassclassmodifiers
  >     jniclasscode                -> imclasscode
  >     jniclassimports             -> imclassimports
  >     jniclassinterfaces          -> imclassinterfaces

- Special variable equivalent names:

  >     $javaclassname              -> $csclassname
  >     $javainput                  -> $csinput
  >     $jnicall                    -> $imcall

An additional special variable, `$module`, is replaced by the module name, as specified in the `%module` directive or `-module` command line option. The intermediary classname has `PINVOKE` appended after the module name instead of `JNI`, for example `modulenamePINVOKE`.

The directory `Examples/csharp` has a number of simple examples. Visual Studio .NET 2003 solution and project files are available for compiling with the Microsoft .NET C# compiler on Windows. If your SWIG installation went well on a Unix environment and your C# compiler was detected, you should be able to type `make` in each example directory, then `ilrun runme` (Portable.NET C# compiler) or `mono runme` (Mono C# compiler) to run the examples. Windows users can also get the examples working using a Cygwin or MinGW environment for automatic configuration of the example makefiles. Any one of the three C# compilers (Portable.NET, Mono or Microsoft) can be detected from within a Cygwin or Mingw environment if installed in your path.