Is there any overhead to declaring a variable within a loop? (C++)

c++ loops variable-declaration
user98188 picture user98188 · Jun 11, 2009 · Viewed 51.6k times · Source

I am just wondering if there would be any loss of speed or efficiency if you did something like this:

int i = 0;
while(i < 100)
{
    int var = 4;
    i++;
}

which declares int var one hundred times. It seems to me like there would be, but I'm not sure. would it be more practical/faster to do this instead:

int i = 0;
int var;
while(i < 100)
{
    var = 4;
    i++;
}

or are they the same, speedwise and efficiency-wise?

Answer

laalto picture laalto · Jun 11, 2009

Stack space for local variables is usually allocated in function scope. So no stack pointer adjustment happens inside the loop, just assigning 4 to var. Therefore these two snippets have the same overhead.

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