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Re: why do some writers declare and define variables separately

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ThosRTanner wrote:

> On Tuesday, October 8, 2013 10:38:14 PM UTC+1, James Kuyper wrote:
>> I prefer to leave variables uninitialized if I cannot initialize them
>> with the value they're supposed to have the next time their value is
>> read. That's because any decent compiler will give you a warning if its
>> analysis of the code flow suggests that there's a possibility of the
>> value of that variable being read before it gets written. Initializing a
>>  variable with a value that's not actually intended to be used turns off
>> that warning, because the compiler doesn't know that you don't intend it
>> to be used.
> 
> I have to say I prefer the other way round, and also to keep the
> declarations in as small a scope as possible (i.e. only in the block,
> rather than declaring every variable ever used at the top of the
> function). Given you have a decent compiler, it should be able to tell you
> that you have assigned a value to a variable without using it as well as
> reading before initialising.

Here is an example of an algorithm where you can neither declare the
variable in the innermost block where it is used nor intitialize with a
good value. I have yet to see a compiler which is able to detect that there
is no read-before-write here.

int f (int x, int *ax, int n)
{
    int i;

    assert (0 < x && x < n);
    for (j = 0; j < n; ++j) {
        if (j > x)
            g (i, ax[j]);
        if (j == x)
            i = h (ax[j]);
    }
}

The variable i must be declared before the loop, and inside the read
of i is statically before the write, but never dynamically before a
previous execution of the body did the write. Unfotunately I forgot
what the algorithm was good for. :-(
-- 
Greetings,
  Jens Schmidt
-- 
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why do some writers declare and define variables separately yoodavid <odimegwudavid@yahoo.fr> - 2013-09-18 16:42 -0500
  Re: why do some writers declare and define variables separately mt <mahdert@gmail.com> - 2013-10-03 13:37 -0500
    Re: why do some writers declare and define variables separately James Kuyper <jameskuyper@verizon.net> - 2013-10-08 16:38 -0500
      Re: why do some writers declare and define variables separately ThosRTanner <ttanner2@bloomberg.net> - 2013-10-22 16:36 -0500
        Re: why do some writers declare and define variables separately Jens Schmidt <Jens.Schmidt-HH@gmx.de> - 2013-10-24 20:10 -0500
        Re: why do some writers declare and define variables separately Francis Glassborow <francis.glassborow@btinternet.com> - 2013-10-24 20:10 -0500
          Re: why do some writers declare and define variables separately Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2013-10-25 19:36 -0500

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