Re: auto_ptr array

From:
"Ben Voigt [C++ MVP]" <rbv@nospam.nospam>
Newsgroups:
microsoft.public.vc.language
Date:
Thu, 3 Apr 2008 10:10:00 -0500
Message-ID:
<OPonOxZlIHA.696@TK2MSFTNGP05.phx.gbl>
George wrote:

Thanks Ben,

puts(), for example, needs a native array.

std::vector<char> myCharacterVector;
....
puts(&myCharacterVector[0]); // works

This won't work with your array of auto_ptrs.

auto_ptr<char> myAutoptrs[20];
....
puts(myAutoptrs[0].get()); // fails


Fail I think you mean runtime error other than compile error. I have
written some code to verify.

How do you think why the heap is corrupted?


I didn't say the heap would be corrupted. I said it would fail. That is,
it would not do what was intended.

[Code]
#include <stdio.h>
#include <memory>

using namespace std;

int main( void )
{
auto_ptr<char> myAutoptrs [2];

char* p1 = new char;
char* p2 = new char;

memcpy (p1, "a", 3);


This line will corrupt the heap because you try to write three bytes into a
buffer which is only one byte.

memcpy (p2, "b", 3);


And again.

myAutoptrs [0].reset (p1);

myAutoptrs [1].reset (p2);


Every string needs to end in a NUL character, make sure to include the
terminator.

puts (myAutoptrs[0].get()); // output a followed by heap corruption
information


Fix the above items and then we can talk about why this line won't work.

return 0;
}
[/Code]

regards,
George

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