Creating a Tcl command

To register a procedure, use the NEWCMD macro. It takes two arguments, the first is the name of the Tcl command to be created, the second is the number of arguments that the Tcl command takes. NEWCMD does the following:

• lodges the commands with the interpreter prior to the execution of tclmain,
• sets up the longjmp label to trap errors,
• checks that the declared number of arguments match the actual number (type checking is beyond the ANSI C Preprocessor!)
• executes the contents of the macro GLOBAL_INIT_HOOK, which can be set to (for example) initialize any global variables from Tcl variables.
• declares a void returning C++ function of the same name as the Tcl command. The arguments are passed via the argc, argv mechanism. All that is required is the body of the function to be put in.

Here is an example.

#include "tcl++.h"

#undef GLOBAL_INIT_HOOK
#define GLOBAL_INIT_HOOK init_funny();

static int funny;

void init_funny()  /* this must be declared before NEWCMD */
{
   if ( 
     Tcl_GetInt(interp, 
        Tcl_GetVar(interp,"funny",TCL_GLOBAL_ONLY), 
        &funny) 
     !=TCL_OK) error("funny not found"); 
}


NEWCMD(silly_cmd,1)
{printf("argv[1]=%s funny=%d\n", argv[1], funny);}