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Message-ID: <46F2F9AE.3060201@roguewave.com>
Date: Thu, 20 Sep 2007 16:52:30 -0600
From: Martin Sebor <sebor@roguewave.com>
Organization: Rogue Wave Software, Inc.
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To: stdcxx-dev@incubator.apache.org
Subject: Re: [PATCH] Add overflow checking to basic_string append and
 push_back
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Travis Vitek wrote:
>  
> 
> Martin,
> 
> I think that you are right in the case of push_back, or when the string
> to append is short. My last testcase didn't prove anything. This one
> does. If you use the current trunk, this prints '4 aaaa' to the console.
> i.e. appending 20 characters to a buffer with 240 should not get you 4,
> should it?
[...]
> template <class _TypeT>
> class Xallocator
> {
> public:
>     typedef unsigned char       size_type;

I suspect the problem might actually be here. Once you define
size_type to a type with a more generous range the test case
passes. I made this and a few other simplifying changes in
the attached program (it's also possible that I messed
something up in the process ;-)

Martin


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#include <cassert>
#include <cstdio>
#include <string>
#include <stdexcept>

template <class T>
struct Xallocator: std::allocator<T>
{
    typedef typename std::allocator<T>::size_type size_type;

    Xallocator (): std::allocator<T>() { } 
    Xallocator (const Xallocator &rhs): std::allocator<T>(rhs) { }
    template <class U>
    Xallocator (const Xallocator<U> &rhs): std::allocator<T>(rhs) { }

    template <class U> 
    struct rebind { typedef Xallocator<U> other; };

    size_type max_size () const { return 255; }
};

typedef std::basic_string<char, std::char_traits<char>, Xallocator<char> >
String;

int main ()
{
    int failed = 0;

    try {
        String a (240, 'a');
        String b (240, 'b');

        // ensure that we will overflow
        assert (a.max_size () < a.size () + 20);

        a.append (b.c_str(), 20);

        std::printf ("%u %s\n", a.size (), a.c_str ());

        failed += 1;
    }
    catch (const std::length_error&) { }
    catch (...) { failed += 1; }

    return failed;
}

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