Re: Memory deallocation does not work.

From:
Kai-Uwe Bux <jkherciueh@gmx.net>
Newsgroups:
comp.lang.c++
Date:
Mon, 12 Feb 2007 18:44:16 -0500
Message-ID:
<eqqu4h$lup$1@murdoch.acc.Virginia.EDU>
Grizlyk wrote:

christophe.chazeau@gmail.com wrote:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <vector>
#include <iterator>

using namespace std;

class Test{
public :
 unsigned char *data ;

 Test(){

 }
 void Go(int taille)
 {

   data = (unsigned char*) malloc(taille);
   printf("malloc : %p\n",data);
 }

 ~Test()
 {
   printf("delete %p\n",data);
   free(data);
 }

};

vector<Test *> v;


It is dangerous - possible memory leak because vector<Test *> does not own
the object pointer point to. Use any RAII memory wrapper (see RAII here:
http://www.hackcraft.net/raii ) instead of Test *

vector<auto_ptr<Test> > v;


That is _bad_ and much more dangerous than vector<Test*>: auto_ptr<> does
not satisfy the requirements for use in a container. Formally, you have
undefined behavior. In practice, you may run into trouble as soon as vector
reallocates.

or give each address (stored in vector<Test *>) to other object, which
will keep object.

{
auto_ptr<Test> owner(new Test);
vector<Test *> v;
    v.push_back(*owner);


*owner is a Test& not a Test*. Do you mean

  v.push_back( owner.operator->() );

}


What happens at this "}"? The auto_ptr<Test> owner destroys the pointee. The
pointer stored in v now is invalid. Any further use is undefined behavior.

What exactly are you trying to to? Should you be headed for automatic memory
management, consider vector< shared_ptr<Test> > or a special container for
pointers that implements some ownership model.

int i = 0 ;

int main()
{

 sleep(10);

 for(i = 0;i<10000;i++)
   {
     Test *t = new Test();
     t->Go(75000);
     v.push_back(t);
   }

 sleep(10);

 vector<Test *>::iterator it;
 for(it=v.begin() ; it!=v.end();it++)


Do you need "it" outside of "for"?


That is a good point.

Try to inplement postfix operator ++, and you will see, that pferix ++ is
better.


"better" in which way?

Should you think of performance, your advice amounts to premature
optimization: chances are that it++ is inlined and optimized to the same
code that ++it would generate.

Avoid repeating function call "v.end()" if you are sure, that the function
will always return the same.


Very likely, this is also premature optimization.

[snip]

Best

Kai-Uwe Bux

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