Command plugins

Command plugins are called by a command interpreter, in a loop.

Usually, the main loop reads from the standard input or a file, line by line. Extension lines are combined when the file is read, so the command code doesn't see them. The string is converted to a “command string”, an object of type “CS”, which is defined in “ap.h”. This command string contains the data, an index showing how far it has been read, and some status.

The command string begins with the name of the command. This is looked up in the “command_dispatcher” using the subscript operator. The dispatcher returns a pointer to a static object that will interpret the command, or a NULL pointer if there is no match.

Then, the method “do_it” is invoked on this object, passing first the command string, with the index advanced to the argument list, and the current “scope” so parameter expressions can be evaluated correctly. If “do_it” returns, it is assumed to have correctly done what was requested. If something is wrong, it may throw an exception.

Each command defines a new class, derived from “CMD” which is defined in “c_comand.h”.

The header file “globals.h” is needed because it contains the declaration of the dispatcher.

Plugins need to #include two files: “c_comand.h” and “globals.h”.

Only one method is needed for each command: ”do_it(CS& Cmd, CARD_LIST* Scope)”.

Declare one static object of this new type, and INSTALL it in the DISPATCHER.

#include "gnucap/c_comand.h"
#include "gnucap/globals.h"
 
class CMD_HELLO : public CMD {
  void do_it(CS& Cmd, CARD_LIST* Scope)
  {
    // code goes here
  }
} so;
DISPATCHER<CMD>::INSTALL d(&command_dispatcher, "hello", &so);