STL Map : Uninitialized Memory Read

Hi,

This is regarding a problem encountered on executing code developed using VS2005 using C++ Standard Libraries.

I have a member in a class of type std::map. The class definition is indicated below (There are some other class members which I am not indicating here so as to not occupy space)

Code:

---

class DataHolder
{
private :
map<DWORD, MyClass *> m_MyMap;

public :
DataHolder()
{
  m_MyMap.clear();
}

void MyMethod()
{
        DWORD j = GetValue();
        map<DWORD,MyClass*>::iterator it = m_MyMap.begin();
        it = m_MyMap.find(j); //Rational Purifier indicated a problem in this line
        if (it == m_MyMap.end())
        {
              printf("Data has not been found in the map");
        }

}
.
.
.
.
.
.
}

---

When the above class is used in the execution of a program and the Rational Purifier tool is being used to analyze memory issues, the following error was indicated in the line marked above :

"Uninitialized Memory Read "

The next level of instructions displayed by the Rational Purifier editor shows the following

Code:

---


    std::_Tree<class std::_Tmap_traits<unsigned long,class MyClass *,struct std::less<unsigned long>,class std::allocator<struct std::pair<unsigned long const ,class MyClass *> >,0> >::_Lbound(unsigned long const &)const  [c:\program files\microsoft visual studio 8\vc\include\xtree.:1174]
                _Nodeptr _Wherenode = _Myhead;    // end() if search fails
       
                while (!_Isnil(_Pnode))
    =>            if (_DEBUG_LT_PRED(this->comp, _Key(_Pnode), _Keyval))
                        _Pnode = _Right(_Pnode);    // descend right subtree
                    else
                        {    // _Pnode not less than _Keyval, remember it

---

The problem is indicated in the line shown by "=> " in the snippet above.

Can someone please provide some clues on why this is being indicated and what would be the possible solution.

You've got something else going on. Can you provide a complete compilable example that reproduces the issue?

gg

[ removed duplicate thread ]

I agree with codeplug. That doesn't mean upload an enormous project file. It means upload a program demonstrating the problem that shows how you are using the std::map and perhaps we will notice something that you are doing incorrectly. At the very least, seeing the complete function or class definition might help. If it is really big, just give us a version that compiles with a simple main function.

I noticed that you are calling clear() on the map in the constructor. Why? It hasn't even been filled with anything yet. It is already empty by default. That isn't the problem but just something else that I noticed.

Hello humble_learner
I agree with kempofighter. We need to see SSCE...um..something like that.
The excerpt by itself looks fine. However, calling clear() inside the constructor body seems questionable.

Quote:

---

Originally Posted by humble_learner

Code:

---

DWORD j = GetValue();

---

---

That could be the source of the error, what if somehow j is not being assigned? Then calling

Code:

---

it = m_MyMap.find(j); //Rational Purifier indicated a problem in this line

---

will cause trouble. Another possible cause is when you assign the iterator to the empty map like you have done below

Code:

---

map<DWORD,MyClass*>::iterator it = m_MyMap.begin();

---

If you recall, T.begin() refers to the first element which in this case has no first element. I'm not sure if that's entirely okay or not though (someone correct me for clarity).

hope this helps

Quote:

---

Originally Posted by potatoCode

If you recall, T.begin() refers to the first element which in this case has no first element. I'm not sure if that's entirely okay or not though (someone correct me for clarity).

---

That should be fine. If the map is empty, then the iterator returned by 'begin' will be equal to the iterator returned by 'end'.

Viggy

Quote:

---

Originally Posted by MrViggy

That should be fine. If the map is empty, then the iterator returned by 'begin' will be equal to the iterator returned by 'end'.

Viggy

---

Hello MrViggy,
Aha I see. Thanks for clearing that up for me :thumb:
bye~