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From: snowball3@usa.net (Mark E.)
Subject: Re: string/cow/algorithm
Date: 1998/08/09
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The program segment under discussion and whether the output is conforming:
>#include <iostream>
>#include <string>
>#include <algorithm>
>using namespace std;
>int main () {
>   string s("Hello world");
>   string c(s);
>   sort(c.begin(), c.end()); // undefined behavior?
>   cout << s << endl;
>   }

jpotter@falcon.lhup.edu (John Potter) wrote:

>Yep, but that program made a copy of a string and sorted it.  The
>result was that the original was also sorted.  There was no "cow"
>done!  I didn't find that reasonable.
>
>I have interpreted your answer as saying the implementation which did
>that nasty thing to me is not conforming.  I am sure glad since it
>would mean that no generic algorithms could be used with strings.
>
>John
>

I have written my own string class using cow and my class produces the same
answer. As far as I'm concerned, s shouldn't also be sorted so my class
would be considered "non-conforming". In my class, I set a flag in the
non-const versions of begin() and end() so when you write a character, a
cow is performed. begin() and end() return pointers to the internal
character array, so if you write:

string s("abc");
string c(s);

*(c.begin()) = 'd'; // Where do I fix this?

The solutions I see to bring my class into conformance is to perform a
clone() type function in the c.begin() statement or write a iterator class
that performs a clone() in operator*.

For reference, my class can be found at
http://members.xoom.com/snowball3/cpp/ )

Mark

-- 
Mark E.: snowball3@usa.net
http://snowball3.home.ml.org/


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