novaBBS - comp.lang.tcl - Tcl_TraceVar() and Tcl

Tcl_TraceVar() and Tcl_Save/RestoreInterpState()

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https://www.novabbs.com/devel/article-flat.php?id=10271&group=comp.lang.tcl#10271

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From: ralf...@gmx.de (Ralf Fassel)
Newsgroups: comp.lang.tcl
Subject: Tcl_TraceVar() and Tcl_Save/RestoreInterpState()
Date: Tue, 29 Nov 2022 17:22:01 +0100
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by: Ralf Fassel - Tue, 29 Nov 2022 16:22 UTC

The manpage for Tcl_TraceVar() states

RESTRICTIONS
A trace procedure can be called at any time, even when there are par-
tially formed results stored in the interpreter. If the trace proce-
dure does anything that could damage this result (such as calling
Tcl_Eval) then it must use the Tcl_SaveInterpState and related routines
to save and restore the original state of the interpreter before it re-
turns.

Does

Tcl_GetVar2(interp, "p1", "p2", TCL_LEAVE_ERR_MSG)

in the trace procedure also count as "possible damage to the interp
result"?

I suspect as much, since if the variable is not found, "an error message
is left in interp's result if the TCL_LEAVE_ERR_MSG flag bit is set."

Vini, vidi, Linux! -- Unknown source

devel / comp.lang.tcl / Tcl_TraceVar() and Tcl_Save/RestoreInterpState()

Subject	Author
Tcl_TraceVar() and Tcl_Save/RestoreInterpState()	Ralf Fassel