Re: How to delete pointers held inside a vector
"David Webber" <dave@musical-dot-demon-dot-co.uk> wrote in message
news:ecrorwcsHHA.4476@TK2MSFTNGP03.phx.gbl...
"ColinG" <csg@mine.com> wrote in message
news:%234xYOecsHHA.3624@TK2MSFTNGP05.phx.gbl...
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;
What value is BUFF_SIZE defined to have?
******************************
MC::MC():
BUFF_SIZE(32)
{
}
******************************
std::vector<tCDV*> m_cDV;
And where is the bit which says
class MC
{
....
};
******************************
Header MC.h contains:
class MC
{
public:
......
.......
MC();
virtual ~MC();
.......
.......
struct tCDV
{
int intC;
long lngR;
bool blnE;
CString strC;
};
tCDV* p_cDV;
const int BUFF_SIZE;
.......
.......
};
******************************
Unit contains the following:
MC::MC():
BUFF_SIZE(32)
{
}
Is BUFF_SIZE now a member of MC?
*********************************
Yes, see definition above in MC.h and initialisation in above constructor
for MC class.
*********************************
MC::Test()
{
p_cDV = new tCDV[BUFF_SIZE];
So p_cDV points to an array of tCDV structures...
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
...and you have now defined the first one...
m_cDV.push_back(p_cDV);
...and copied the pointer to it into the first element of your vector.
***************************************
Yes. The reason for using a vector is because I have the following 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[BUFF_SIZE];
p_cDV->intC = cc;
p_cDV->lngR = cr;
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];
You have allocated memory for BUFF_SIZE tCDVs and initilised the first
one. You have copied the pointer to the first one into the vector.
***************************************
Please see the above for loop (my apologies for not including this in my
initial posting).
****************************************
I attempted to iterate through the vector: m_cDV
How do you mean "iterate"? It only has one element!
********************************************
Please see the above for loop (my apologies for not including this in my
initial posting).
The iteration in the destructor for MC class was as below:
for (int x = 0; x < m_cDV.size(); x++) {
delete[] m_cDV[x];
}
********************************************
(via the destructor of class MC), deleting the pointers p_cDV but to no
avail. So, I scrapped the iteration code.
[You need to appreciate the difference between deleting an object and
deleting a pointer.]
You only defined one pointer to an array. The only way to get rid of it
is
delete [] p_cDV ;
******************************
Please see the above for loop (my apologies for not including this in my
initial posting).
******************************
Do NOT try and destroy the first element by using the destructor on the
first object in your vector (and deleting the pointer to the first object
will not help). Which means do NOT try to delete the vector!
Please can someone assist me in resolving this problem.
I think you need to resolve the difference bertween a standard array, and
what a vector class does.
With vector you define each element individually and then add it to the
vecor with push_back. You don't need a normal array as well. Unless you
have a good reason, you don't need to use a vector of pointers to
objects, but a vector of objects.
************************************
After reading Tom's reply. I use:
in MC.h:
std::vector<tCDV> m_cDV;
in MC.ccp:
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;
p_cDV->lngR = cr;
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);
}
in destructor for MC class:
for (int x = 0; x < m_cDV.size(); x++) {
delete[] m_cDV[x];
}
which results 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
Thanks.
C
************************************
Hope this points you in the right direction.
Dave
--
David Webber
Author of 'Mozart the Music Processor'
http://www.mozart.co.uk
For discussion/support see
http://www.mozart.co.uk/mzusers/mailinglist.htm