Calling TCL from C Link to heading

Starting with working example, we can see that Tcl_CreateInterp and Tcl_Eval are the only two Tcl calls.

#include <stdio.h>
#include <tcl.h>

main (int argc, char *argv[]) {

        Tcl_Interp *myinterp;
        char *action = "set a [expr 5 * 8]; puts $a";
        int status;

        printf ("Your Program will run ... \n");

        myinterp = Tcl_CreateInterp();
        status = Tcl_Eval(myinterp,action);

        printf ("Your Program has completed\n");
}

And compilation command

gcc main.c -I /usr/include/tcl8.6 -ltcl

Docs says Tcl_CreateInterp is

Tcl_CreateInterp creates a new interpreter structure and returns a token for it. The token is required in calls to most other Tcl procedures, such as Tcl_CreateCommand, Tcl_Eval

And Tcl_Eval

Tcl_Eval is similar to Tcl_EvalObjEx except that the script to be executed is supplied as a string instead of a value and no compilation occurs.

Calling C from TCL (TCL extension) Link to heading

On the other side, TCL provides an interface to call C from TCL same as built-in procs.

For this to work, we need to 2 functions:

• Registration called when shared object is loaded
• proc implementation

Docs describes Tcl_CreateObjCommand

Tcl_CreateObjCommand deletes any existing command name already associated with the interpreter (however see below for an > exception where the existing command is not deleted). It returns a token that may be used to refer to the command in subsequent > calls to Tcl_GetCommandName. If name contains any :: namespace qualifiers, then the command is added to the specified namespace; > otherwise the command is added to the global namespace. If Tcl_CreateObjCommand is called for an interpreter that is in the > process of being deleted, then it does not create a new command and it returns NULL. proc should have arguments and result that > match the type Tcl_ObjCmdProc:

typedef int Tcl_ObjCmdProc( ClientData ta, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]);

#include <stdio.h>
#include <tcl.h>

static int hello(ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj *const objv[])
{
	printf("Hello World\n");
	return TCL_OK;
}

int Hello_Init(Tcl_Interp *interp)
{
	Tcl_CreateObjCommand(interp, "hello", hello, NULL, NULL);
	return TCL_OK;
}

gcc commands to compile shared object

	gcc -c hello.c -I /usr/include/tcl8.6
	gcc -shared -o hello.so hello.o -ltcl

Finally, we need to load the shared object with TCL load.

load ./hello.so
hello

Side note, Docs mentions Hello_Init has to be called SOMEHING_Init for load command to execute it while loading the shared object. According to docs, SOMETHING is package name .

C-TCL-C chaining Link to heading

for fun, I tried chaining C calling TCL and TCL calling C.

This is main.c (the main driver)

#include <stdio.h>
#include <tcl.h>

void main (int argc, char *argv[]) {

        Tcl_Interp *myinterp;
        char *action = "load ./hello.so;hello";
        int status;

        printf ("Your Program will run ... \n");

        myinterp = Tcl_CreateInterp();
        status = Tcl_Eval(myinterp,action);

        printf ("Your Program has completed\n");
}

and hello.c same as before.