C++ Efficency of variable declaration

Question

I have a curiosity. I would like to know if it is more efficient this code

int a(0);
for(int i=0;i!=10;++i){
    a=0;
    for(int j=0;j!=10;++j){
        // perform some operations on a
    }
}

or this code

for(int i=0;i!=10;++i){
    int a(0);
    for(int j=0;j!=10;++j){
        // perform some operations on a
    }
}

or it is exactly the some in term of performance. I understand that the answer may depend on the compiler and its inner optimization technique but I am curios to understand if there is any difference.

Thank you, Marco.

Depends on the implementation. If the implementers have done their job there should be no difference and any deteriorations are going to be taken care of the optimizer. — 101010, Jun 04 '14 at 15:22

score 3 · Accepted Answer · answered Jun 04 '14 at 15:25

3

In any modern C++ compiler there's no difference what-so-ever.

answered Jun 04 '14 at 15:25

Paul Evans

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+1 for answering the C++ question (in the former question, there is very much to read) – Wolf Jun 04 '14 at 15:36

C++ Efficency of variable declaration

1 Answers1