1Tcl_SaveResult(3) Tcl Library Procedures Tcl_SaveResult(3)
2______________________________________________________________________________
6
8 Tcl_SaveInterpState, Tcl_RestoreInterpState, Tcl_DiscardInterpState,
9 Tcl_SaveResult, Tcl_RestoreResult, Tcl_DiscardResult - save and restore
10 an interpreter's state
11
13 #include <tcl.h>
14 Tcl_InterpState
16 Tcl_SaveInterpState(interp, status)
17 int
19 Tcl_RestoreInterpState(interp, state)
20 Tcl_DiscardInterpState(state)
22 Tcl_SaveResult(interp, savedPtr)
24 Tcl_RestoreResult(interp, savedPtr)
26 Tcl_DiscardResult(savedPtr)
28
30 Tcl_Interp *interp (in) Interpreter for which state
31 should be saved.
32 int status (in) Return code value to save as
34 part of interpreter state.
35 Tcl_InterpState state (in) Saved state token to be restored
37 or discarded.
38 Tcl_SavedResult *savedPtr (in) Pointer to location where inter‐
40 preter result should be saved or
41 restored.
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43
46 These routines allows a C procedure to take a snapshot of the current │
47 state of an interpreter so that it can be restored after a call to │
48 Tcl_Eval or some other routine that modifies the interpreter state. │
49 There are two triplets of routines meant to work together. │
50 The first triplet stores the snapshot of interpreter state in an opaque │
52 token returned by Tcl_SaveInterpState. That token value may then be │
53 passed back to one of Tcl_RestoreInterpState or Tcl_DiscardInterpState, │
54 depending on whether the interp state is to be restored. So long as │
55 one of the latter two routines is called, Tcl will take care of memory │
56 management. │
57 The second triplet stores the snapshot of only the interpreter result │
59 (not its complete state) in memory allocated by the caller. These rou‐ │
60 tines are passed a pointer to a Tcl_SavedResult structure that is used │
61 to store enough information to restore the interpreter result. This │
62 structure can be allocated on the stack of the calling procedure. │
63 These routines do not save the state of any error information in the │
64 interpreter (e.g. the -errorcode or -errorinfo return options, when an │
65 error is in progress). │
66 Because the routines Tcl_SaveInterpState, Tcl_RestoreInterpState, and │
68 Tcl_DiscardInterpState perform a superset of the functions provided by │
69 the other routines, any new code should only make use of the more pow‐ │
70 erful routines. The older, weaker routines Tcl_SaveResult, Tcl_Restor‐ │
71 eResult, and Tcl_DiscardResult continue to exist only for the sake of │
72 existing programs that may already be using them. │
73 Tcl_SaveInterpState takes a snapshot of those portions of interpreter │
75 state that make up the full result of script evaluation. This include │
76 the interpreter result, the return code (passed in as the status argu‐ │
77 ment, and any return options, including -errorinfo and -errorcode when │
78 an error is in progress. This snapshot is returned as an opaque token │
79 of type Tcl_InterpState. The call to Tcl_SaveInterpState does not │
80 itself change the state of the interpreter. Unlike Tcl_SaveResult, it │
81 does not reset the interpreter. │
82 Tcl_RestoreInterpState accepts a Tcl_InterpState token previously │
84 returned by Tcl_SaveInterpState and restores the state of the interp to │
85 the state held in that snapshot. The return value of Tcl_RestoreIn‐ │
86 terpState is the status value originally passed to Tcl_SaveInterpState │
87 when the snapshot token was created. │
88 Tcl_DiscardInterpState is called to release a Tcl_InterpState token │
90 previously returned by Tcl_SaveInterpState when that snapshot is not to │
91 be restored to an interp. │
92 The Tcl_InterpState token returned by Tcl_SaveInterpState must eventu‐ │
94 ally be passed to either Tcl_RestoreInterpState or Tcl_DiscardInterp‐ │
95 State to avoid a memory leak. Once the Tcl_InterpState token is passed │
96 to one of them, the token is no longer valid and should not be used │
97 anymore.
98 Tcl_SaveResult moves the string and object results of interp into the
100 location specified by statePtr. Tcl_SaveResult clears the result for
101 interp and leaves the result in its normal empty initialized state.
102 Tcl_RestoreResult moves the string and object results from statePtr
104 back into interp. Any result or error that was already in the inter‐
105 preter will be cleared. The statePtr is left in an uninitialized state
106 and cannot be used until another call to Tcl_SaveResult.
107 Tcl_DiscardResult releases the saved interpreter state stored at
109 statePtr. The state structure is left in an uninitialized state and
110 cannot be used until another call to Tcl_SaveResult.
111 Once Tcl_SaveResult is called to save the interpreter result, either
113 Tcl_RestoreResult or Tcl_DiscardResult must be called to properly clean
114 up the memory associated with the saved state.
115
118 result, state, interp
119Tcl 8.1 Tcl_SaveResult(3)