malloc(): memory corruption (fast) [Cant seem to figure this out] on FC5 + G++ 4.1.0

[g***@gmail.com]

Hi, I have the following code that is giving this error, I cant
simplify the code, I was just testing some theory for something we are
doing and was getting an issue here. Please someone point out whats
wrong with my code.


[code]
class MsgData
{
char* data;
int size;

public:

MsgData(long l)
{
count++;
size = 0;
data = NULL;
operator=(l);
}

MsgData(char* d)
{
count++;
size = 0;
data = NULL;
if(d)
{
size = strlen(d);
data = new char[size];
strcpy(data, d);
printf("MsgData(%s) @%d\n", d, data);
}
}

MsgData(char* d, int s)
{
//printf("MsgData(%s, %d)\n", d, s);
data = NULL;
count++;
size = s;
data = new char[size];
printf("MsgData(%s, %d) @%d\n", d, s, data);

if(d)
{
memcpy(data, d, size);
data[size] = 0;
}
}

MsgData()
{
//printf("MsgData()\n");
count++;
data = NULL;
size = 0;
}

MsgData(const MsgData& m)
{
//printf("MsgData(MsgData(%s, %d))\n", m.data, m.size);
count++;
data = NULL;
size = 0;
copy(m);
}

~MsgData()
{
count--;
printf("~MsgData(%s, %d) @%d [count=%d]\n", data, size, data,
count);
delete [] data;
data = NULL;
//printf("count:%d\n", count);
}

MsgData& copy(char* d, int l)
{
printf("copy(%s, %d) @%d\n\n", d, l, data);
MsgData tmp(d, l);
copy(tmp);
}

MsgData& copy(char* d)
{
printf("copy(%s) @%d\n\n", d, data);
return copy(d, strlen(d));
}

MsgData& copy(const MsgData& rhd)
{
printf("copy(MsgData(%s, %d))\n\n", rhd.data, rhd.size);
if(data)
{
delete [] data;
data = NULL;
size = 0;
}

if(rhd.size)
{
size = rhd.size;
data = new char[size];
memcpy(data, rhd.data, size);
data[size] = 0;
}

return *this;
}

MsgData& operator=(long l)
{
//printf("operator=(%l)\n", l);
char tmp[16];
sprintf(tmp, "%d", l);
return copy(tmp);
}

MsgData& operator=(char* rhd)
{
printf("operator=(%s)\n\n", rhd);
if(!rhd)
return *this;

MsgData tmp(rhd);
return copy(tmp);
}

MsgData& operator=(MsgData rhd)
{
printf("operator=(MsgData(%s, %d)) @%d\n\n", rhd.data, rhd.size,
data);
return copy(rhd);
}

MsgData operator+(MsgData& rhd)
{
printf("operator+(MsgData(%s, %d) @%d\n\n", rhd.data, rhd.size,
data);
MsgData msg;
msg.append(*this);
msg.append(rhd);
printf("newly created append: %s\n", msg.tostr());
return msg;
}

MsgData& append(char* rhd)
{
MsgData msg(rhd);
return append(msg);
}

MsgData& append(MsgData& rhd)
{
if(data && size)
{
if(rhd.data && rhd.size)
{
char* tmp = data;
data = new char[size+rhd.size];
memcpy(data, tmp, size);
memcpy(data+size, rhd.data, rhd.size);
size +=rhd.size;
data[size] = 0;
delete [] tmp;
tmp = NULL;
}
return *this;
}

if(rhd.data && rhd.size)
{
return copy(rhd);
}

return *this;
}

MsgData operator+(char* str)
{
/*char* tmp = data;
data = new char[size + strlen(str)];
if(data)
memcpy(data, tmp, size);
memcpy(data+size, str, strlen(str));
size += strlen(str);
delete [] tmp;
return *this;*/

/*printf("operator+(%s) to %s\n", str, data);
MsgData tmp(0, size+strlen(str));
if(data)
sprintf(tmp.tostr(), "%s%s", data, str);
else
strcpy(tmp.tostr(), str);
return tmp;*/

printf("operator+(%s)\n\n", str);
MsgData msg(str);
return operator+(msg);
}

char operator[](int index)
{
//printf("operator[%d]\n", index);
if(data && (index >=0 && index < size))
return data[index];

return 0;
}

bool operator==(char* rhd)
{
MsgData tmp(rhd);
return operator==(tmp);
}

bool operator==(MsgData& rhd)
{
if(!data || !rhd.data)
return false;

if(size != rhd.size)
return false;

if(!strncmp(data, rhd.data, size))
return true;

return false;
}

char*& tostr()
{
//printf("tostr()\n");
return data;
}
};

[/code]


And now the driver code which is giving me the issue

[code]
int main()
{
MsgData m1, m2, m3, m4, m5;
m1 = "m1";
m2 = "m2";
m3 = "m3";

m4 = m4 + m1 + "123";
//m4 = m4 + m1 + m2 + m3 + "123" + "1";
printf("%s = %d----------------------------------------%d\n",
m4.tostr(), 0,0);
m4 = m4 + m1 + "123";
printf("%s = %d----------------------------------------%d\n",
m4.tostr(), 1,1);
m4 = m4 + " " + m1 + "123";
m4 = m4 + " " + m1 + "123";
m4 = m4 + " " + m1 + "123";
printf("%s = %d----------------------------------------%d\n",
m4.tostr(), 2,2);


printf("m4=%s\n", m4.tostr());
}
[/code]

or if I change those m4 lines to then it again core dumps but if i
comment the 2nd line " m4 = m4 + m1 + "123"; " it works??

[code]
m4 = m4 + m1 + m2 + m3 + "123" + "1";
printf("%s = %d----------------------------------------%d\n",
m4.tostr(), 0,0);
m4 = m4 + m1 + "123";
printf("%s = %d----------------------------------------%d\n",
m4.tostr(), 1,1);
m4 = m4 + " " + m1 + "123";
printf("%s = %d----------------------------------------%d\n",
m4.tostr(), 2,2);
[/code]

I will get the same problem...I cant seem to figure whats the
difference in doing this over and over again.

Please someone help! I just cant seem to figure this out.

Thanks

Ankur

[trm]

Post by g***@gmail.com
Hi, I have the following code that is giving this error, I cant
simplify the code, I was just testing some theory for something we are
doing and was getting an issue here. Please someone point out whats
wrong with my code.
[code]
class MsgData
{
char* data;
int size;
MsgData(long l)
{
count++;

'count' has not been defined anywhere.

Post by g***@gmail.com
size = 0;
data = NULL;

It's better to use initializer lists for this.

Post by g***@gmail.com
operator=(l);
}

Without looking to see what operator=() actually does, I will say
that it's an unclear way of writing this. Better would be to use a
private helper function, which both MsgData() and operator=() can
call internally.

Post by g***@gmail.com
MsgData(char* d)

This should probably be (const char *d), unless you intend to
modify whatever d points to.

Post by g***@gmail.com
{
count++;
size = 0;
data = NULL;

Same comments as previously.

Post by g***@gmail.com
if(d)
{
size = strlen(d);

You have a signedness mismatch and a possible size mismatch here.

Post by g***@gmail.com
data = new char[size];

You probably meant: new char[size + 1]...

Post by g***@gmail.com
strcpy(data, d);

...yes, that's what you meant. The line above has just corrupted
some memory somewhere.
Undefined behaviour. Use %p, not %d, to printf() pointers.

Post by g***@gmail.com
}
}

[Lots of similar quality code snipped.]

Post by g***@gmail.com
Please someone help! I just cant seem to figure this out.

I suggest that you study a C++ textbook, and start out with basic
(that is, short and uncomplicated) exercises. You are trying to do
too many things at once here. You're also using mainly C idioms
in place of conceptually simpler C++ idioms. It also appears that
you're using a pre-standard compiler, which will limit the usefulness
of any advice you receive here.

[Ron Natalie]

Post by g***@gmail.com
Hi, I have the following code that is giving this error, I cant
simplify the code, I was just testing some theory for something we are
doing and was getting an issue here. Please someone point out whats
wrong with my code.
[code]
class MsgData
{
char* data;
int size;

If you just declared this as
std::string data;

You'd avoid having to mismanipulate string data (and possibly
even writing your own bug-ridden copy constructor, assignment
op, and destructors).