.PP
The following is a minimal extension:
.PP
.CS
#include <tcl.h>
#include <stdio.h>
static int fooCmd(void *clientData,
        Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]) {
        Tcl_Interp *interp, Tcl_Size objc, Tcl_Obj *const objv[]) {
    printf("called with %d arguments\en", objc);
    return TCL_OK;
}
int Foo_Init(Tcl_Interp *interp) {
    if (Tcl_InitStubs(interp, "8.1", 0) == NULL) {
	return TCL_ERROR;
    }
    printf("creating foo command");
    Tcl_CreateObjCommand(interp, "foo", fooCmd, NULL, NULL);
    Tcl_CreateObjCommand2(interp, "foo", fooCmd, NULL, NULL);
    return TCL_OK;
}
.CE
.PP
When built into a shared/dynamic library with a suitable name
(e.g. \fBfoo.dll\fR on Windows, \fBlibfoo.so\fR on Solaris and Linux)
it can then be loaded into Tcl with the following: