NAME

       Tcl_SaveInterpState,  Tcl_RestoreInterpState,  Tcl_DiscardInterpState, Tcl_SaveResult, Tcl_RestoreResult,
       Tcl_DiscardResult - save and restore an interpreter's state

SYNOPSIS

       #include <tcl.h>

       Tcl_InterpState
       Tcl_SaveInterpState(interp, status)

       int
       Tcl_RestoreInterpState(interp, state)

       Tcl_DiscardInterpState(state)

       Tcl_SaveResult(interp, savedPtr)

       Tcl_RestoreResult(interp, savedPtr)

       Tcl_DiscardResult(savedPtr)

ARGUMENTS

       Tcl_Interp *interp (in)                Interpreter for which state should be saved.

       int status (in)                        Return code value to save as part of interpreter state.

       Tcl_InterpState state (in)             Saved state token to be restored or discarded.

       Tcl_SavedResult *savedPtr (in)         Pointer to location where interpreter result should  be  saved  or
                                              restored.
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DESCRIPTION

       These  routines allows a C procedure to take a snapshot of the current state of an interpreter so that it
       can be restored after a call to Tcl_Eval or some other  routine  that  modifies  the  interpreter  state.
       There are two triplets of routines meant to work together.

       The   first   triplet  stores  the  snapshot  of  interpreter  state  in  an  opaque  token  returned  by
       Tcl_SaveInterpState.  That token value may then be  passed  back  to  one  of  Tcl_RestoreInterpState  or
       Tcl_DiscardInterpState,  depending  on whether the interp state is to be restored.  So long as one of the
       latter two routines is called, Tcl will take care of memory management.

       The second triplet stores the snapshot of only the interpreter result (not its complete state) in  memory
       allocated  by  the  caller.  These routines are passed a pointer to Tcl_SavedResult that is used to store
       enough information to restore the interpreter result.  Tcl_SavedResult can be allocated on the  stack  of
       the  calling procedure.  These routines do not save the state of any error information in the interpreter
       (e.g. the -errorcode or -errorinfo return options, when an error is in progress).

       Because the routines Tcl_SaveInterpState, Tcl_RestoreInterpState, and  Tcl_DiscardInterpState  perform  a
       superset  of  the functions provided by the other routines, any new code should only make use of the more
       powerful routines.  The older, weaker routines Tcl_SaveResult, Tcl_RestoreResult,  and  Tcl_DiscardResult
       continue to exist only for the sake of existing programs that may already be using them.

       Tcl_SaveInterpState  takes a snapshot of those portions of interpreter state that make up the full result
       of script evaluation.  This include the interpreter result, the return code  (passed  in  as  the  status
       argument, and any return options, including -errorinfo and -errorcode when an error is in progress.  This
       snapshot is returned as an opaque token of type Tcl_InterpState.  The call  to  Tcl_SaveInterpState  does
       not  itself  change  the  state  of  the  interpreter.   Unlike  Tcl_SaveResult,  it  does  not reset the
       interpreter.

       Tcl_RestoreInterpState accepts a Tcl_InterpState token previously  returned  by  Tcl_SaveInterpState  and
       restores  the  state  of  the  interp  to  the  state  held  in  that  snapshot.   The  return  value  of
       Tcl_RestoreInterpState is the status value originally passed to  Tcl_SaveInterpState  when  the  snapshot
       token was created.

       Tcl_DiscardInterpState   is   called   to   release   a  Tcl_InterpState  token  previously  returned  by
       Tcl_SaveInterpState when that snapshot is not to be restored to an interp.

       The  Tcl_InterpState  token  returned  by  Tcl_SaveInterpState  must  eventually  be  passed  to   either
       Tcl_RestoreInterpState  or Tcl_DiscardInterpState to avoid a memory leak.  Once the Tcl_InterpState token
       is passed to one of them, the token is no longer valid and should not be used anymore.

       Tcl_SaveResult moves the string and value results of interp into  the  location  specified  by  statePtr.
       Tcl_SaveResult clears the result for interp and leaves the result in its normal empty initialized state.

       Tcl_RestoreResult moves the string and value results from statePtr back into interp.  Any result or error
       that was already in the interpreter will be cleared.  The statePtr is left in an uninitialized state  and
       cannot be used until another call to Tcl_SaveResult.

       Tcl_DiscardResult  releases  the saved interpreter state stored at statePtr.  The state structure is left
       in an uninitialized state and cannot be used until another call to Tcl_SaveResult.

       Once  Tcl_SaveResult  is  called  to  save  the   interpreter   result,   either   Tcl_RestoreResult   or
       Tcl_DiscardResult must be called to properly clean up the memory associated with the saved state.

KEYWORDS

       result, state, interp