Re: access violation question

From:

"Daniel T." <daniel_t@earthlink.net>

Newsgroups:

comp.lang.c++

Date:

Mon, 27 Dec 2010 17:31:38 -0500

Message-ID:

<daniel_t-DA5D64.17313827122010@70-3-168-216.pools.spcsdns.net>

Thomas <user@nl.invalid> wrote:

On 27-12-2010 22:28, Ian Collins wrote:

On 12/28/10 10:20 AM, Paavo Helde wrote:

Thomas<user@nl.invalid> wrote in news:ifav7r$i6v$1@speranza.aioe.org:

On 27-12-2010 17:49, AnonMail2005@gmail.com wrote:

Please post your code.

Here is the code, that will compile on Codeblocks (gcc compiler), but
leads to an error during execution.

First error seems to be in the function terugtel():

while (terugtel != vint.size())
{
terugtel++;
if (vint[terugtel] == terugtel + 1)

Here terugtel becomes equal to vint.size() eventually, thus vint
[terugtel] is illegal.

This was easily catched by MSVC++2010 Debug mode build, BTW.

You pipped me to the post! Also easily spotted by Solaris dbx.

Thomas, you should find your self a decent debugger!

As it happens, this problem doesn't arise, because the vector<int>s with
length n in this program are by definition filled with permutations of
the integer range [1..n] (not [0..n-1]). The terugtel() function worked
fine in all previous programs that used it.

Sorry Thomas, you are wrong. If the terugtel() function has been in
previous programs, it didn't work there either.

I took your code and did to it what I suggested you do:

inline unsigned int terugtel(vector<unsigned int>& vint)
{
   unsigned int terugtel = 0, vangst = 0;
   while (terugtel != vint.size())
   {
      terugtel++;
      if (vint.at(terugtel) == terugtel + 1)
      {
         reverse (vint.begin(), vint.begin()+terugtel+1);
         terugtel = 0;
         ++vangst;
      }
   }
   return vangst;
}

The at() function threw an exception when terugtel equaled vint.size().
This shows that there is a problem with this code.