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memory question

Posted on 1998-11-27
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Last Modified: 2010-04-01
Is there a difference between:
MyFunc()
{
 if(...)
  return;
 int i;
 ....
}
and:
MyFunc()
{
 int i;
 if(...)
  return;
  ....
}
concerning the stack/memory ??
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Question by:nil_dib
2 Comments
 
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jkr earned 50 total points
ID: 1178748
No, there's _no_ differnce (except in the notation), as the stack is always set up when the function is entered. I.e. the stack space for all local varaibles is allocated before the first code statement is executed.
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Expert Comment

by:nietod
ID: 1178749
I would have to dissagree somewhat.  To the best of my knowledge that is entirely implimentation defined.  That is, it is up to the designer of the compiler.    In fact, I believe (again I'm not sure) that it is common practice in many implimentations to set up multiple stack frames  in a function that has nested scrope, thus a function like

MyFunc()
{
    {
       int i;
    }
}

would actually set up and destroy a second stack frame in some cases.  There is no telling how such a compiler would handle the case you presented.

I think you can be sure of this.  There is goign to be no significant difference in execution speed between the two.  This is because operations required to provide space for the integer are insignificant.  This would not be true if the variable in question had a constructor that took considerable time to run, for example, if the constructor read from a file.  In that case, the first version would be faster.

You have this quesions 2 times.  You might want to delete the other.
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