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critcl_devguide(n) 3.2 doc "C Runtime In Tcl (CriTcl)"


critcl_devguide - Guide To The CriTcl Internals

Table Of Contents


Be welcome to the C Runtime In Tcl (short: CriTcl), a system for embedding and using C code from within Tcl scripts.


This document is a guide for developers working on CriTcl, i.e. maintainers fixing bugs, extending the package's functionality, etc.

Please read

  1. CriTcl - License,

  2. CriTcl - How To Get The Sources, and

  3. CriTcl - The Installer's Guide

first, if that was not done already.

Here we assume that the sources are already available in a directory of the readers choice, and that the reader not only know how to build and install them, but also has all the necessary requisites to actually do so. The guide to the sources in particular also explains which source code management system is used, where to find it, how to set it up, etc.

Playing with CriTcl

Note that the sources of CriTcl, should the reader have gotten them, also contain several examples show-casing various aspects of the system. These demonstration packages can all be found in the sub-directory "examples/" of the sources.

Lots of smaller examples can be found in the document Using CriTcl, an introduction to CriTcl by way of a of examples. These focus more on specific critcl commands than the overall picture shown by the large examples mentioned in the previous paragraph.

Developing for CriTcl

Architecture & Concepts

The system consists of two main layers, as seen in the figure below, plus a support layer containing general packages the system uses during operation.


  1. At the top we have an application built on top of the core packages, providing command line access to the second and third usage modes, i.e. Generate Package and Generate TEA Package.

  2. Below that is the core package providing the essential functionality of the system, plus various utility packages which make common tasks more convenient.

  3. Lastly a layer of supporting packages, mostly external to critcl.


    For this pure-Tcl package to be fast users should get one of several possible accelerator packages:

    1. tcllibc

    2. Trf

    3. md5c



To develop for critcl the following packages and applications must be available in the environment. These are all used by the build.tcl helper application.


A Tcl application provided by Tcllib, for the validation and conversion of doctools-formatted text.


A Tcl application provided by Tklib, for the validation and conversion of diagram-formatted figures into raster images.

Do not confuse this with the Gnome dia application, which is a graphical editor for figures and diagrams, and completely unrelated.


A Tcl package provided by Tcllib, providing file system utilities.

vfs::mk4, vfs

Tcl packages written in C providing access to Tcl's VFS facilities, required for the generation of critcl starkits and starpacks.

Directory structure


This helper application provides various operations needed by a developer for critcl, like regenerating the documentation, the figures, building and installing critcl, etc.

Running the command like

	./build.tcl help

will provide more details about the available operations and their arguments.


This directory contains the documentation sources, for both the text, and the figures. The texts are written in doctools format, whereas the figures are written for tklib's dia(gram) package and application.


This directory contains the documentation converted to regular manpages (nroff) and HTML. It is called embedded because these files, while derived, are part of the git repository, i.e. embedded into it. This enables us to place these files where they are visible when serving the prject's web interface.


These files are a standard testsuite based on Tcl's tcltest package, with some utility code snarfed from Tcllib.

This currently tests only some of the stubs::* packages.


These files (except for "all.tcl" and "testutilities.tcl") are example files (Tcl with embedded C) which can be run through critcl for testing.

TODO for a maintainers: These should be converted into a proper test suite.

Package Code, General structure
Package Code, Per Package

The Tcl code implementing the package.


The configuration file for the standard targets and their settings.


Various C code snippets used by the package. This directory also contains the copies of the Tcl header files used to compile the assembled C code, for the major brnaches of Tcl, i.e. 8.4, 8.5, and 8.6.


The Tcl code implementing the package.


The Tcl code implementing the package.


The Tcl code implementing the package.


C code template used by the package.


The Tcl code implementing the package.


C code template used by the package.


A set of non-public (still) packages which provide read and write access to and represent Tcl stubs tables. These were created by taking the "genStubs.tcl" helper application coming with the Tcl core sources apart along its internal logical lines.


Arjen Markus' work on a critcl/Fortran. The code is outdated and has not been adapted to the changes in critcl version 3 yet.


These are all external packages whose code has been inlined in the repository for easier development (less dependencies to pull), and quicker deployment from the repository (generation of starkit and -pack).

TODO for maintainers: These should all be checked against their origin for updates and changes since they were inlined.


Jean Claude Wippler, Steve Landers, Andreas Kupries

Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report them at https://github.com/andreas-kupries/critcl/issues. Ideas for enhancements you may have for either package, application, and/or the documentation are also very welcome and should be reported at https://github.com/andreas-kupries/critcl/issues as well.


C code, Embedded C Code, calling C code from Tcl, code generator, compile & run, compiler, dynamic code generation, dynamic compilation, generate package, linker, on demand compilation, on-the-fly compilation


Glueing/Embedded C code