Re: How to delete pointers held inside a vector

From:

"ColinG" <csg@mine.com>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 18 Jun 2007 22:22:42 +0100

Message-ID:

<#CRhS7esHHA.508@TK2MSFTNGP02.phx.gbl>

"Tom Widmer [VC++ MVP]" <tom_usenet@hotmail.com> wrote in message
news:u9zvptcsHHA.400@TK2MSFTNGP02.phx.gbl...

ColinG wrote:

Hi,

I have a class named MC.

Header contains the following:

struct tCDV
{
  int intC
  long lngR;
  bool blnE;
  CString strC;
};
tCDV* p_cDV;

const int BUFF_SIZE;

std::vector<tCDV*> m_cDV;

Why do you have a vector of pointers to objects. Why not just:

std::vector<tCDV> m_cDV;

tCDV meets the requirements for storage in a vector (it's copyable and
assignable).

*******************************
std::vector<tCDV> m_cDV;

This has resulted in the following error:

MC.cpp(59) : error C2440: 'delete' : cannot convert from 'struct MC::tCDV'
to ''
No user-defined-conversion operator available that can perform this
conversion, or the operator cannot be called
MC.cpp(59) : fatal error C1903: unable to recover from previous error(s);
stopping compilation
*******************************

Unit contains the following:

MC::MC():
BUFF_SIZE(32)
{
}

MC::Test()
{
p_cDV = new tCDV[BUFF_SIZE];

You create an array of 32 tCDV objects here, but below you only access the
first one. Is this intentional? Are you sure you didn't mean:
p_cDV = new tCDV;

*******************************
I now have:

p_cDV = new tCDV;
*******************************

   p_cDV->intC = cc; //cc initialised elsewhere in program
   p_cDV->lngR = cr; //cr initialised elsewhere in program
   p_cDV->blnE = file.read_bool(); // file.read_bool() initialised
elsewhere in program
   p_cDV->strC = file.read_string(); // file.read_string() initialised
elsewhere in program

  m_cDV.push_back(p_cDV);
}

All the above works fine. My problem is that I receive memory leaks on
program exit and the debugger points to:

    p_cDV = new tCDV[BUFF_SIZE];

I attempted to iterate through the vector: m_cDV (via the destructor of
class MC), deleting the pointers p_cDV but to no avail.

You created them with new[], so you need to delete with delete[]:

delete[] m_cDV[i];

*******************************
In the destuctor, I now have:

for (int x = 0; x < m_cDV.size(); x++) {
delete[] m_cDV[x];
}

*******************************

So, I scrapped the

iteration code.

Please can someone assist me in resolving this problem.

The best solution is not to use pointers at all (which will often give
faster as well as shorter code). The next best solution is to use either a
pointer container class, or a smart pointer class. That way you don't have
to manually delete the objects at all. See:

http://www.boost.org/libs/ptr_container/doc/ptr_container.html
http://www.boost.org/libs/smart_ptr/shared_ptr.htm

I have browsed these links. So, I guess my earlier comment:

std::vector<tCDV> m_cDV;

This has resulted in the following error:

MC.cpp(59) : error C2440: 'delete' : cannot convert from 'struct MC::tCDV'
to ''
        No user-defined-conversion operator available that can perform this
conversion, or the operator cannot be called
MC.cpp(59) : fatal error C1903: unable to recover from previous error(s);
stopping compilation

relates to the need to not use pointers or use either a pointer container
class, or a smart pointer class.

My reason for using a vector was because:

p_cDV = new tCDV;

is contained with a nested loop:

int num = file.read_int();
  for (j=0; j < num; j++) {
    cc = file.read_ushort(); // file.read_ushort() initialised elsewhere in
program
    cr = file.read_ushort(); // file.read_ushort() initialised elsewhere in
program

   p_cDV = new tCDV;
   p_cDV->intC = cc; //cc initialised elsewhere in program
   p_cDV->lngR = cr; //cr initialised elsewhere in program
   p_cDV->blnE = file.read_bool(); // file.read_bool() initialised elsewhere
in program
   p_cDV->strC = file.read_string(); // file.read_string() initialised
elsewhere in program
   m_cDV.push_back(p_cDV);

Anyway, I will look in more detail at those links.

Thanks.

Colin

Tom