Re: "Scoping" variables the middle of their "natural" scope - RAII - is it a good practice?

Ronald Landheer-Cieslak <>
Sun, 17 Jan 2010 07:19:09 CST
ManicQin wrote:

Hello everybody,
Let me explain what I mean,

In my job I find many times the next "pattern"

void foo()
//some code
    { //"re-scoping"
    char sTmp[256] = "";
    //some code
//some code

sometimes the "re-scoping" was made to keep sTmp in his reservation
and sometimes it's just and old
"if scope" that was deleted and the scopes were left on intention (or
not by intention), my point is that dropping the scopes will -usually-
wont harm the -logical- flow of the code.
(it can cause compile problems because of redefinition but the code
itself will be autonomous)

When looking on projects and examples in the internet I find more and
more "scoped" classes (RAII),
ScopeGuard, ScopedTimer, ScopedBarrierEnd ,ScopedForking , auto_ptr
(and his many friends) and the list is long...

Now, when dropping the "re-scoping" of a class I can harm the -
logical- flow of the code.
(Well you can always add comments ... and hope someone will read them,
or you can use macros such as
#define SCOPETIMER_START(name) { ScopeTimer name();
but I always find that using such macros to "ugly up" your code...)

Is it a good practice to "re-scope"? (RAII classes)
Are there any guide lines for RAII classes?

IMO, it really depends on what you're scoping. In the example you
provided, there's only an array of chars being "re-scoped", so unless
you have another one with the same name a bit further down the road, I
don't see a reason to do that. OTOH, scope guards and scoped locks are
definitely something you might want to keep in a smaller scope -
especially scoped locks. The alternative would be to trigger their
"action" (whatever it usually does when it goes out of scope) where your
scope would have ended..

I agree on the macro, by the way: they do make the code uglier. In any
case, IMO again, scopes like that should be documented in the code.


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