Tk_Init can add Tk to an interpreter and make a new Tk application.
#include < tk.h >
Tcl_Interp *interp (in)
Interpreter in which to load Tk. Tk should not already be loaded in this interpreter.
Tk_Init is the package initialization procedure for Tk. It is normally invoked by the Tcl_AppInit procedure for an application or by the load command. Tk_Init adds all of Tk's commands to interp and creates a new Tk application, including its main window. If the initialization is successful Tk_Init returns TCL_OK; if there is an error it returns TCL_ERROR. Tk_Init also leaves a result or error message in interp->result.
If there is a variable argv in interp, Tk_Init treats the contents of this variable as a list of options for the new Tk application. The options may have any of the forms documented for the wish application (in fact, wish uses Tk_Init to process its command-line arguments).