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