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'''[Tcl Tutorial Index]'''
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**General information on Tcl and C**

Tcl can be regarded as a powerful configuration language sitting on top of a bunch of [C] functions. Tcl's original purpose (according to Tcl's inventor John Ousterhout (see [How do I use the Tcl C API?])), was to create a standard language that could be embedded in applications. The intent was that Tcl would be accessed only via its C API.

***Extending Tcl***
This C API can be use to extend Tcl, giving it new commands and new functionality (see [Extending Tcl]). The recommended way for this is to use Tcl's Extension Architecture [TEA], a set of guidelines and techniques for the distribution, configuration, compilation, and installation of Tcl extensions. TEA comes with a "sample extension" showing how to do things:

   * [SampleExtension]

Regardless whether you are writing an extension in C or Tcl, here is some more information:

   * [How to build good packages]
   * [Tips for writing quality software]
   * [How to Write Quality Documentation]
   * [C-like include in tcl]
   * [Solutions for Extension Building]
   * [Tcl extension prototype - proto.cpp] (in C++)
   * [Invoking Tcl commands from Cplusplus]
   * [Useful C Commands For Tcl]
   * [HOWTO: Make a Tcl Extension Thread-Safe] (examples of thread-safe extensions: [Thread-safe Tcl Extensions]
   * [Extending Tcl] (most info on that page is also included here)
   

****Hello world****
To see how extendind Tcl works in practice, you should have a look at the typical 'Hello world' example:

   * [Hello World as a C extension]
   * [Building the Hello C Extension using Visual Studio 2010 express]

There are also other examples of small extensions in C:

   * [RPN C extension for Tcl]
   * [rphoto] (fast photo image rotation)


****More on TEA****
The Tcl Extension Architecture is a whole story in itself. TEA is largely defined by the tcl.m4 file in [tclconfig], along with the `configure.in` and `Makefile` files in the sample extension. A `makefile.vc` and `rules.vc` file is also included for Windows builds. TEA describes a directory layout both for the source distribution and for files installed as part of the extension. Files in the source distribution of an extension are laid out such that platform-specific components live in a directory dedicated to that platform. The version of TEA is defined by the TEA_VERSION variable in the tcl.m4 file in [tclconfig].

Here are some pages dealing with TEA:

   * [TEA]
   * [TEA2]
   * [TEA3]
   * [Converting your Tcl extension to TEA2]
   * [TEA: a summary of trying to use it, Vince Darley]
   * [Annotated 10 steps to success with TEA]

Examples of existing extensions using TEA are: [Tktable], [TclX], [itcl/itk].

****Extending Tcl (with C) from within Tcl****
Going one step further, you can even extend Tcl with a C function that is written inside the Tcl script where you need it:

   * [Critcl]
   * [Critcl builds C extensions on-the-fly]
   * [tcltcc]
   * [Extending Tcl in C from Tcl]

***Embedding Tcl***
Of course, you can also still use Tcl as embedded language in you application. Here are some pages about this, including customization of [tclsh] itself:

   * [How to embed Tcl in C applications]
   * [Combining Fortran and Tcl in one program]
   * [Building a custom tclsh]
   * [Experiences with a custom tclsh]

Embedding Tcl typically involves using the C API function [Tcl_Init].

**The Tcl C API**
All the Tcl C API functions have manual pages. However, the Wiki has also a bit of information on some of the API functions. Start with the list of function here:

   * [Tcl C API]

There are some commin design principles in the C API which you read about here: [Tcl C API Design Principles].

Some special information on certain aspects of the Tcl C API can be found here:

   * [Using Tcl_ListObj and his friends]
   * [Tcl Handles]
   * [Tcl_GetStringResult() forward compatibility] (direct use of interp->result is now forbidden)

***About the string interface and the Tcl_Obj interface***

**The Tk C API**
Just as Tcl, also Tk has its own C API. Here is a list (probably incomplete) with more information on at least a few of the Tk C functions:

   * [Tk C API]

Here is some more information (and examples) on extending Tk:

   * [Adding Tk to an existing Xt program]


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[Category Tcl Library] | [Category Tk Library] | [Category Tutorial]

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'''[Tcl Tutorial Index]'''
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