Scroll to navigation

Tcl_SaveResult(3tcl) Tcl Library Procedures Tcl_SaveResult(3tcl)
 


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.
    
    

    
 

    

  




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 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_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 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_DiscardResult must be called to
  properly clean up the memory associated with the saved state.



KEYWORDS

result, state, interp



  

    8.1
    Tcl