c++ - Faster to reuse a variable defined in a common scope or redefine it in each inner scope? -

c++ specifically, if matters, imagine answer lies in assembly code somehow.

if have multiple blocks in common scope (say, function) each use variable of same type, faster define variable in common scope , reinitialise in each block, or redefine , initialise in each of blocks (or there no fundamental difference)?

example:

int i;  {//block 1     = somefunction();     ... }  {//block 2     = someotherfunction();     ... } 

versus

{//block 1     int = somefunction();     ... }  {//block 2     int = someotherfunction();     ... } 

if i pod type (like int shown in example), there no difference @ all.

if i of type has nontrivial constructor or assignment operator exciting, there might huge difference , you'd have compare appropriate constructors , assignment operators do. if both blocks entered, you'll need consider destructor well.

in general, shouldn't worry it. take cleaner approach , declare variable in restricted scope possible, close first use possible, , refactor out if profiler tells performance problem spot.