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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_RestoreRe-sult, Tcl_RestoreResult,
       sult, 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_SaveIn- |
       terpState.  That token value may then be passed back to one  of  Tcl_RestoreInterpState  or  Tcl_Dis- |
       cardInterpState, depending on whether the interp state is to be restored.  So long as one of the lat- |
       ter 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 a Tcl_SavedResult structure |
       that is used to store enough information to restore the interpreter result.  This  structure  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_Dis- |
       cardResult 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_Restor- |
       eInterpState 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 object 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 object 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_Dis-cardResult Tcl_DiscardResult
       cardResult must be called to properly clean up the memory associated with the saved state.


KEYWORDS
       result, state, interp



Tcl                                                  8.1                                   Tcl_SaveResult(3)