Question

is there a Performance difference between this:

int test;
void Update()
{
    test +=2;
}

and this:

void Update()
{
    int test;
    test +=2;
}

—

int main()
{
    while(true)
        Update();
}

I ask because the second Code is better to read (you don’t need to declare it at Class headers), so i would use it if the performance is not lower.

Answer 1

It is highly unlikely that there is a performance difference between the two snippets only profiling your code can tell reliably but there is a important functional difference tha you should consider here.

If your test variable is needed only inside the function update() then you must declare it inside the function. That way the variable has a limited scope inside the function.The lifetime of such a local variable is limited to the scope where it resides.i.e. Within the function body, till the closing brace}.

If at all you want your test variable to maintain state across function calls then it can be a local static variable declared inside the function.

Declaring test outside the function makes it an global variable. And it can be accessible in any function in the same file.Also being a global variable it lifetime extends till end of program.