Introduction to Tcl-Cpp

Tcl-Cpp is a package for interfacing C++ code to Tcl. I have found Tcl to be an enormously useful interactive shell for experimenting with and debugging C++ code. However, writing the wrappers to convert C++ code functions into tcl-callable functions is sometimes onerous and often highly repetitive; using Tcl-Cpp, all you need to do is write a simple interface description file, and all the messy stuff is handled for you!

Contents for these pages

• Introduction
• Features
• Downloading
• An example: floatVectors and floatRefs
• Reference manual
• Implementation details and design philosophy

Introduction

Tcl-Cpp is based on Dean Sheenan's ObjectTcl. Most of its functionality comes from the ObjectTcl core. However, my requirements were sufficiently different from those addressed by ObjectTcl that creating my own version was the best solution.

Specifically, while Dean's wanted all the objects in his system to be properly `owned' by the Tcl part of the application -- thereby avoiding the problem of stale references to objects that had been deleted -- I was prepared to pass the responsibility of resource management on to the user in return for the ability to create Tcl wrappers around object references on-the-fly as they turned up at run-time.

The net effect of this is that while the Tcl equivalents of C++ objects in ObjectTcl are subclasses of the C++ objects (allowing C++ virtual methods to be overridden with Tcl code), in Tcl-Cpp the Tcl objects are separate entities that contain pointers to C++ objects (which allows Tcl to run the specialized virtual functions of objects accessed through base classes).

Tcl-Cpp consists of a stand-alone translator program that converts the interface description file into C++ source files, and a library to link with your Tcl application that provides access to the new commands defined in the interface description.

Features

Tcl-Cpp provides the following advantages over ObjectTcl:

• descriptive object names - i.e. myObject9 rather than 100109e0.
• Tk-style constructor syntax - i.e.
  ClassName $objectName args
  rather than
  set objectName [otclNew ClassName args].
• Tcl wrapper creation as necessary on the fly for object pointers and references that appear from within the C++ code.
• Optional arguments (with default values) for methods and constructors
• Configuration options may be appended to constructor lines (like Tk) i.e.
  ClassName myinstance -slotname value
• `Dummy' arguments allow for Tk-style specification of constructor arguments e.g. Array::Array(int rows, int cols) can be accessed from Tcl as Array arrayName -rows $rows -cols $cols
• Small fragments of Tcl may be specified to be executed when accessing slots or for `dummy' methods, e.g. method Size -dummy {return "$rows $cols"}
• Tcl wrappers for abstract base classes and correct access to virtual functions from within Tcl. (ObjectTcl could only call virtual functions redefined in Tcl; Tcl-Cpp cannot make Tcl subclasses of C++ objects).
• extended interface description language (cdl) including:
  • slot declaration - like a method declaration, except declaring accessible object attributes.
  • -cast type modifier to coerce a type change.
  • -new type modifier to force a returned object or string to be copied.
• config and cget commands to access the declared slots in normal Tk-style syntax.
• Itcl-like syntax - supports <Classname> #auto and <Classname> :: <classmethod>
• Error messages report all recognized commands for each object, for rapid error correction in interactive usage.
• Inheritance of Tcl access to methods and slots of C++ superclasses declared as parents in the interface description file. (ObjectTcl only inherited within Tcl).

Downloading the source

The latest version should be available in my FTP directory at ICSI. The current version is tclcpp-latest.tar.gz.

Go on to the examples page.

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