Silly loop question

[laertius]

Probably a stupid question... but is it generally more efficient to declare a variable within a loop, i.e.

for(i = 0; i<10; i++) {
int n;
n = someArray[i]; // for instance
... do some stuff with n
}

or outside of it, i.e.

int n;
for(i = 0; i<10; i++) {
n = someArray[i]; // for instance
... do some stuff with n
}

I'd always assumed the latter, but I've seen some examples of the former in what I thought was pretty optimised code.

Thanks.

[Rashakil Fol]

In C it should not matter, if all the other operations are the same.

In C++, the latter style is more efficient for any datatype that has a constructor (because 'objname n;' actually causes code to be run). It should still be no better for ints though.

[cbastard]

I think the first one would be better if the variable is not to be used outside the loop.because in the former the variable will be destroyed as the loop ends.There by releasing the stack space.So it is more memorily efficient.

[Rashakil Fol]

The variable just goes "out of scope," which is a programming language issue.

If it is not used after a certain point in the subroutine, it's not as if the compiler isn't going to use that memory or that register for something else, unless it doesn't need to.

[cbastard]

If the variable is used outside the loop(means defined by latter).Compiler will definetly not use that memory unless it is overwritten by user.this memory will not be added to heap.