DAMAGE: after Normal block (#45)

[Meghavvarnam]

Hi all,

I just joined this group and am new to VC++. I wrote the code following
the next para in C++ and used VC++ 6.0 Enterprise Edition to build and
test.

I had the following error message because of an exception that gets
thrown when I call delete [] ipAddress; in the destructor -
~TrapDestination () :

"DAMAGE: after Normal block (#45)"

// ~~~~~~~~~~~
// plugIn.h
// ~~~~~~~~~~~
#include <memory>
#include <iostream>
#include <exception>
#include <assert.h>
using namespace std;

typedef char* pchar;

class TrapDestination {
private:
pchar ipAddress;
int port;
pchar communityName;
int snmpVersion;
pchar templateFileName;
void (*old_unexpected) ();

public:
TrapDestination () : ipAddress (NULL), communityName (NULL),
templateFileName (NULL) { //old_unexpected =
set_unexpected:my_unexpected­);
}
~TrapDestination () throw () {
cout << "TrapDestination Destructor" << endl;
if (ipAddress)
delete [] ipAddress;
if (communityName)
delete [] communityName;
if (templateFileName)
delete [] templateFileName;

//set_unexpected(old_unexpecte­d); // restore org
handler
if (uncaught_exception())
cout << "uncaught_exception() is TRUE" << endl;

else
cout << "uncaught_exception() is FALSE" <<
endl;
}

char *getIPAddress () throw () { return ipAddress; }
int getPort () throw () { return port; }
char *getcommunityName () throw () { return communityName; }
int getsnmpVersion () throw () { return snmpVersion; }
char *gettemplateFileName () throw () { return
templateFileName; }

void setIPAddress (char *ipAddr="") throw () {
ipAddress = (pchar) new char(strlen (ipAddr) + 1);
if (ipAddress)
strcpy (ipAddress, ipAddr);
}

void setPort (int aPort=162) { port = aPort; }

void setcommunityName (char *aCommunityName="public") {
communityName = (pchar) new char (strlen
(aCommunityName) + 1);
if (communityName)
strcpy (communityName, aCommunityName);
}

void setsnmpVersion (int snmpVer=2) { snmpVersion = snmpVer; }

void settemplateFileName (char *templFileName="") {
templateFileName = (pchar) new char (strlen
(templFileName) + 1);
if (templateFileName)
strcpy (templateFileName, templFileName);
}
};

class SnmpTrapGen {
private:
char *ipAddress;
int port;
char *community;
int snmpVersion;
public:
SnmpTrapGen (char *ipAddress=NULL, int port=162, char
*community="public", int snmpVersion=2){
}
~SnmpTrapGen () {
if (ipAddress)
delete [] ipAddress;
if (community)
delete [] community;
}

sendTrap (char *alertToSend);
char *getIPAddress () { return ipAddress; }
int getPort () { return port; }
char *getcommunity () { return community; }
int getsnmpVersion () { return snmpVersion; }

void setIPAddress (char *ipAddr="") {
ipAddress = new char (strlen (ipAddr) + 1);
if (ipAddress)
strcpy (ipAddress, ipAddr);
}
void setPort (int aPort=162) { port = aPort; }
void setcommunity (char *aCommunity="public") {
community = new char (strlen (aCommunity) + 1);
if (community)
strcpy (community, aCommunity);
}
void setsnmpVersion (int snmpVer=2) { snmpVersion = snmpVer; }

};


// ~~~~~~~~~~~~
// plugIn.cpp
// ~~~~~~~~~~~~

#include "net-snmp\net-snmp-config.h"
#include "net-snmp\net-snmp-includes.h"
#include "plugIn.h"

void local_terminator() {
cout << "terminate called local_terminator !!!" << endl;
exit(1);
}

void (*old_terminate)();

void my_unexpected () {
// This cannot return - instead it can either call std::terminate() or
throw an exception

cout << "Am in my_unexpected " << endl;
}

int main (int argc, char **argv) {
try {
TrapDestination td;

old_terminate = set_terminate(local_terminator­);
td.setIPAddress ("127.0.0.1");
td.setcommunityName ();
td.settemplateFileName ("tempname");
cout << "IP address = " << td.getIPAddress () << endl;
printf ("communityName = %s.\n", td.getcommunityName
());
printf ("templateFileName = %s.\n",
td.gettemplateFileName ());
return 0;
} catch (bad_exception const &) {
printf("Caught bad_exception\n"); // though such an
exception was
never thrown
return 0;
} catch (...) {
cout << "Inside main's catch all" << endl;
return 0;
}
}


Any light on :

1. Why is delete causing this exception to be thrown could be helpful.
2. What the solution for this is.

will be great!

Just to add, an earlier post similar to this scenario had a response
that while allocating space for a string using new, make sure you add 1
for the '\0'. However I have taken care of doing that in my code and
yet I have this exception when it hits the delete.

I really need help from an expert.

Thank you,
Meghavvarnam Satish

 

[Victor Bazarov]

I just joined this group and am new to VC++. I wrote the code following
the next para in C++ and used VC++ 6.0 Enterprise Edition to build and
test.

Unless the behaviour is specific to that compiler and you tried other ones
and found that out, the compiler you used is irrelevant. We don't discuss
products here. We discuss the language.

I had the following error message because of an exception that gets
thrown when I call delete [] ipAddress; in the destructor -
~TrapDestination () :

"DAMAGE: after Normal block (#45)"
[...]

This is usually caused by memory overrun (writing beyond the bounds of
an array) or by using an uninitialised pointer (which by coincidence just
points to some real memory). Use a memory debugging tool (something like
BoundsChecker or Purify or Insure++) to find the problem, or do it in the
debugger, manually. Your goal is to learn your tools, not to use this
newsgroup as your remote debugger.

V

 

[John Carson]

[snip]

void setIPAddress (char *ipAddr="") throw () {
ipAddress = (pchar) new char(strlen (ipAddr) + 1);
if (ipAddress)
strcpy (ipAddress, ipAddr);
}

The syntax for new is wrong (here and everywhere else that you use it). It
should be

ipAddress = new char[strlen (ipAddr) + 1];

i.e., use square brackets, not round brackets (your cast to pchar is
redundant, but that is not what is causing the problem). Square brackets
give an array of chars, which is what you want. Round brackets are for when
you are specifying the argument for the constructor of a single object.

 

[CI]

You could try to use auto_ptr rather than using raw pointers. I dont
see any specific reason why you want to use raw pointer here.
Ik

 

[Meghavvarnam]

Hey John!

I tried your suggestion. And made changes where ever I call new for the
character pointers.

It worked fine this time around!!! Thank you so much !!!

I infact looked back into "The C++ Pragraming Language" Third Edition
by Bjarne Stroustup, pg. 131 where he says for a built in type T, T(e)
is equivalent to (T) e ; e being any value. This implies that "for
built-in types", T(e) is not safe.

So my earlier code -
ipAddress = (pchar) new char (strlen (ipAddr) + 1);
was actually looked at as
ipAddress = (pchar) new (char) strlen (ipAddr) + 1;

Thus resulting in an int being type casted to a char and then being
passed to new. And thus we had an implementation defined behaviour over
there.

Thanks a lot again!!!
Megh

 

[Meghavvarnam]

Hi,

My original code had auto_ptr instead of a plain char *.

However when I debugged and looked at the call stack, the destructor
would call delete. delete would then call free. free would then call
_free_dbg. And then I would get that exception.

I doubted auto_ptr and to make it simpler, I used char *. However as
you all know now, the behaviour did not change.

However now I will use auto_ptr and see how it behaves. We wont need to
call delete at that point of time specifically, because our friend
auto_ptr would do that for us.

Will be back with the update folks !

Thank you!
Megh

 

[Victor Bazarov]

My original code had auto_ptr instead of a plain char *.

However when I debugged and looked at the call stack, the destructor
would call delete. delete would then call free. free would then call
_free_dbg. And then I would get that exception.

I doubted auto_ptr and to make it simpler, I used char *. However as
you all know now, the behaviour did not change.

However now I will use auto_ptr and see how it behaves. We wont need to
call delete at that point of time specifically, because our friend
auto_ptr would do that for us.

Will be back with the update folks !

'auto_ptr' is not going to work for you. It does NOT work with arrays.
And you apparently need arrays.

Stop using the array of char and switch to 'std::string'.

V

 

[Meghavvarnam]

Hi again,

Below is the auto_ptr version. It works fine too !!!

// ~~~~~~~~
// plugIn.h
// ~~~~~~~~

#include <memory>
#include <iostream>
#include <exception>
#include <assert.h>
using namespace std;

typedef auto_ptr <char> pchar;

//typedef char* pchar;

class TrapDestination {
private:
pchar ipAddress;
int port;
pchar communityName;
int snmpVersion;
pchar templateFileName;
void (*old_unexpected) ();

public:
TrapDestination () : ipAddress (NULL), communityName (NULL),
templateFileName (NULL) {
}
~TrapDestination () throw () {
cout << "TrapDestination Destructor" << endl;
//set_unexpected(old_unexpected); // restore org handler
if (uncaught_exception())
cout << "uncaught_exception() is TRUE" << endl;
else
cout << "uncaught_exception() is FALSE" << endl;
}

char *getIPAddress () throw () { return ipAddress.get (); }
int getPort () throw () { return port; }
char *getcommunityName () throw () { return communityName.get (); }
int getsnmpVersion () throw () { return snmpVersion; }
char *gettemplateFileName () throw () { return templateFileName.get
(); }

void setIPAddress (char *ipAddr="") throw () {
ipAddress = (pchar) new char [strlen (ipAddr) + 1];
if (ipAddress.get ())
strcpy (ipAddress.get (), ipAddr);
ipAddress.get ()[strlen(ipAddr)] = '\0';
}

void setPort (int aPort=162) { port = aPort; }

void setcommunityName (char *aCommunityName="public") {
communityName = (pchar) new char [strlen (aCommunityName) + 1];
if (communityName.get ())
strcpy (communityName.get (), aCommunityName);
}

void setsnmpVersion (int snmpVer=2) { snmpVersion = snmpVer; }

void settemplateFileName (char *templFileName="") {
templateFileName = (pchar) new char [strlen (templFileName) + 1];
if (templateFileName.get ())
strcpy (templateFileName.get (), templFileName);
}
};


class SnmpTrapGen {
private:
char *ipAddress;
int port;
char *community;
int snmpVersion;
public:
SnmpTrapGen (char *ipAddress=NULL, int port=162, char
*community="public", int snmpVersion=2){
}
~SnmpTrapGen () {
if (ipAddress)
delete [] ipAddress;
if (community)
delete [] community;
}

sendTrap (char *alertToSend);

char *getIPAddress () { return ipAddress; }
int getPort () { return port; }
char *getcommunity () { return community; }
int getsnmpVersion () { return snmpVersion; }

void setIPAddress (char *ipAddr="") {
ipAddress = new char [strlen (ipAddr) + 1];
if (ipAddress)
strcpy (ipAddress, ipAddr);
}
void setPort (int aPort=162) { port = aPort; }
void setcommunity (char *aCommunity="public") {
community = new char [strlen (aCommunity) + 1];
if (community)
strcpy (community, aCommunity);
}
void setsnmpVersion (int snmpVer=2) { snmpVersion = snmpVer; }
};

 

[Meghavvarnam]

Hi all:

Apologies for the confusion in my previous post. Am pasting the above
piece of code that works again. Have reformatted it.

Please note the usage of the member function get () to get the address
of an auto_ptr variable.

// ~~~~~~~~~
// plugIn.h
// ~~~~~~~~~

#include <memory>
#include <iostream>
#include <exception>
#include <assert.h>
using namespace std;

typedef auto_ptr <char> pchar;

class TrapDestination {
private:
pchar ipAddress;
int port;
pchar communityName;
int snmpVersion;
pchar templateFileName;
void (*old_unexpected) ();

public:
TrapDestination () : ipAddress (NULL), communityName (NULL),
templateFileName (NULL) {
//old_unexpected = set_unexpected:my_unexpected);
}
~TrapDestination () throw () {
cout << "TrapDestination Destructor" << endl;

if (uncaught_exception())
cout << "uncaught_exception() is TRUE" << endl;
else
cout << "uncaught_exception() is FALSE" << endl;
}

char *getIPAddress () throw () { return ipAddress.get (); }
int getPort () throw () { return port; }
char *getcommunityName () throw () { return communityName.get (); }
int getsnmpVersion () throw () { return snmpVersion; }
char *gettemplateFileName () throw () { return templateFileName.get
(); }

void setIPAddress (char *ipAddr="") throw () {
ipAddress = (pchar) new char [strlen (ipAddr) + 1];
if (ipAddress.get ())
strcpy (ipAddress.get (), ipAddr);
ipAddress.get ()[strlen(ipAddr)] = '\0';
}

void setPort (int aPort=162) { port = aPort; }

void setcommunityName (char *aCommunityName="public") {
communityName = (pchar) new char [strlen (aCommunityName) + 1];
if (communityName.get ())
strcpy (communityName.get (), aCommunityName);
}

void setsnmpVersion (int snmpVer=2) { snmpVersion = snmpVer; }

void settemplateFileName (char *templFileName="") {
templateFileName = (pchar) new char [strlen (templFileName) + 1];
if (templateFileName.get ())
strcpy (templateFileName.get (), templFileName);
}

};


class SnmpTrapGen {
private:
char *ipAddress;
int port;
char *community;
int snmpVersion;
public:
SnmpTrapGen (char *ipAddress=NULL, int port=162, char
*community="public", int snmpVersion=2){
}
~SnmpTrapGen () {
if (ipAddress)
delete [] ipAddress;
if (community)
delete [] community;
}

sendTrap (char *alertToSend);

char *getIPAddress () { return ipAddress; }
int getPort () { return port; }
char *getcommunity () { return community; }
int getsnmpVersion () { return snmpVersion; }

void setIPAddress (char *ipAddr="") {
ipAddress = new char [strlen (ipAddr) + 1];
if (ipAddress)
strcpy (ipAddress, ipAddr);
}
void setPort (int aPort=162) { port = aPort; }
void setcommunity (char *aCommunity="public") {
community = new char [strlen (aCommunity) + 1];
if (community)
strcpy (community, aCommunity);
}
void setsnmpVersion (int snmpVer=2) { snmpVersion = snmpVer; }

};

Thank you again
Megh

 

[Meghavvarnam]

Hi V,

When we declare, we use auto_ptr. As you might already know, auto_ptr
is a mechanism that provides ownership to take care of releasing the
memory that we allocate with a new.

However, while calling new, specifically for an inbuilt type, we
specify the size of memory that we request with in square brackets.

And once the memory is allocated, we could use it like an array. We
could index into it too.

Anyway thanks for your suggestion about the 'std::string'

Regards,
Megh

 

[Victor Bazarov]

When we declare, we use auto_ptr. As you might already know, auto_ptr
is a mechanism that provides ownership to take care of releasing the
memory that we allocate with a new.

However, while calling new, specifically for an inbuilt type, we
specify the size of memory that we request with in square brackets.

And once the memory is allocated, we could use it like an array. We
could index into it too.

That would be wrong. 'auto_ptr' destroys the object using 'delete'.
If you allocate it using 'new[]', you _have_to_ use 'delete[]' and not
'delete'. So, 'auto_ptr' is not a suitable mechanism here.

[...]

V

 

[Victor Bazarov]

Apologies for the confusion in my previous post. Am pasting the above
piece of code that works again. Have reformatted it.

Please note the usage of the member function get () to get the address
of an auto_ptr variable.
[...]

Your code has undefined behaviour. If it happens to work on your
system, it's no indication that it's correct.

V