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)