Chapter 41. C++ encapsulation of a Tcl API subset

The tclPlus library provides a C++ object oriented encapsulation of a large subset of the Tcl application programming interface. This section provides reference material for this class library.

Sections of the NSCLDAQ and SpecTcl products both make extensive use of this library. It is therefore distributed with both prodcuts, from a common source base. Therefore, there are two ways to link to this library. First, using SpecTcl:

            
g++ -o yourprogram yoursources  \
               -L${SPECTCLHOME}/lib -ltclPlus -lException
            
            

Second, using nscldaq, replace ${SPECTCLHOME} with the top level directory of your NSCLDAQ installation, e.g. /usr/opt/daq/8.1.

Some brief descriptions of the primary classes in this library follow:

CTCLApplication

This is a base class for complete applications that extend the Tcl/Tk interpreter. By appropriately subclassing it you can build your own standalong extended Tcl/Tk interpreters.

CTCLException

The Tcl/Tk API use return codes to indicate error conditions. This is error prone. The tclPlus library converts these return codes in to thrown exceptions of the type CTCLException. To handle these exceptions properly requires use of C++ try/catch blocks. A code fragment example of this is provided in the CTCLException(3) manpage.

CTCLInterpreter

The CTCLInterpreter object is at the core of the library. It is a wrapping of a Tcl_Interp* along with member functions that access many functions that logically operate on a Tcl interpreter.

CTCLInterpreterObject

The CTCLInterpreterObject wraps objects that require an interpreter to function correctly. It is a base class for many of the classes in the library. It provides common services for those objects.

CTCLList

In Tcl scripting, lists play a key role in providing a structured data type. The CTCLList object can be created on a string believed to be a list, and used to split a list into its elements or merge a set of words into a list.

CTCLObject

Tcl has the philosophy that everything can be treated as if it were a string. In older versions of the interpreter, everything was a string. This led to a great deal of inefficiency converting other data types to and from strings. The Tcl_Obj type was created to reduce this inefficiency and to reduce the amount of string copying that was necessary to invoke commands.

A Tcl_Obj is an object that stores the string representation and another representation type for a Tcl interpreter entity. Tcl_Obj also provides for object sharing with copy on modify semantics. This reduces much of the string copying overhead that was previously associated with executing Tcl interpreter commands.

The CTCLObject is a wrappig of a Tcl_Obj along with functions that operate on the underlying object.

CTCLObjectProcessor

Key to the concept of the Tcl interpreter as an application scripting language is the ability to add new commands to the interpreter that are application specific. The CTCLObjectProcessor class is an abstract base class that, when subclassed and instantiated adds new commands to the interpreter.

CTCLVariable

The CTCLVariable class provides access to Tcl script variables.

CItemConfiguration and CConfigurableObject while not actually Tcl objects provide infrastructure that is useful in the context of extension to a Tcl interpreter. Specifically the creation and maintanance of commands that generate objects that have some configuration associated with them. Configuration is expressed as a set of name value pairs. While all of the values have string representation, validators can be associated with configuration parameters to enforce type safeness, and range checking.

A rich set of predefined validators are supplied with the package, and custom validators can also be written and used.