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Tcl_SaveResult(3)           Tcl Library Procedures           Tcl_SaveResult(3)

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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

Tcl                                   8.1                    Tcl_SaveResult(3)