Morgan Stanley Interview Question for Financial Software Developers


Country: United States
Interview Type: In-Person




Comment hidden because of low score. Click to expand.
3
of 3 vote

many errors in your code.
for instance. ctor should never return and its parameter must be const reference.

- jianbozhu May 12, 2012 | Flag Reply
Comment hidden because of low score. Click to expand.
3
of 3 vote

#include<iostream>

template<class T>
class sharedPtr
{
        T* ShrdPtr;
        mutable int* refCount;

public:
        sharedPtr( T* ptr ) { ShrdPtr = ptr; refCount = new int(); *refCount = 1; }
        ~sharedPtr( )
        {
                std::cout << "inside destructor refCount = " << *refCount << "\n";
                if( --(*refCount) == 0 )
                        delete ShrdPtr;
        }
        T& operator=( const sharedPtr& ptr );
        sharedPtr( const sharedPtr& ptr );
        T* operator->( ) { return ShrdPtr; }
        T& operator*() { return *ShrdPtr; }
};

template<class T>
T& sharedPtr<T>::operator=( const sharedPtr& ptr )
{
        std::cout << "inside assignment operator\n";
        this->ShrdPtr = ptr.ShrdPtr;
        (*(ptr.refCount))++;
        this->refCount = ptr.refCount;
        return *this;
}

template<class T>
sharedPtr<T>::sharedPtr( const sharedPtr& ptr )
{
        std::cout << "inside copy constructor\n";
         this->ShrdPtr = ptr.ShrdPtr;
        (*(ptr.refCount))++;
        this->refCount = ptr.refCount;
}


int main( int argc, char* argv[] )
{
        sharedPtr<int> p = new int;
        {
                sharedPtr<int> q = p;
        }
        return 0;
}

- sachin jain July 12, 2012 | Flag Reply
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1
of 1 vote

memory leak in destructor. refcount memory is never free

- Ivan September 18, 2013 | Flag
Comment hidden because of low score. Click to expand.
1
of 1 vote

Why should refCount be mutable?

- Chandan October 19, 2015 | Flag
Comment hidden because of low score. Click to expand.
0
of 0 vote

Here is my Implementation of shared ptr:
// shared_pointer.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>
#include <exception>

using namespace std;

template <class T> class sh_ptr
{
private:
T* ptr;
static int count;

public:
sh_ptr() {
ptr = new T;
count++;
cout << "count = " << count << endl;
}
~sh_ptr() {
// check count before deleting the pointer
cout << " count before = " << count << endl;
count--;
cout << " count after = " << count << endl;


if ( !count)
{

if (ptr) delete ptr;
ptr = NULL;
}
}

// implement sssignment and copy operation because shared pointer
// does copy and assignment. So it is named as shared pointer

// make sure that the copy constructor will invoke additional
// pointer to that heap memory and one additional counter
// no deep copy is required. For assignment operator
// we may require a deep copy as they already point to two different memory location.
// or we may not write a assignment operator
// We have to implement operator-> to exhibit the pointer behavior.
sh_ptr(sh_ptr& d){
ptr = d.ptr;
count++ ;

}

sh_ptr& operator=(sh_ptr& d){
// here is a memory leak for new, so first delet the new
// before assigning the pointer to another memory location
delete d.ptr;
ptr = d.ptr;
count++ ;
return *this;

}



void fun()
{
cout << " this is a fun" << endl;
}
sh_ptr<T>* operator->()
{
return (this);
}

};

template < class T> int sh_ptr<T>::count=0;


int main(int argc, char* argv[])
{

{
sh_ptr<int> obj;
obj->fun();
sh_ptr<int> obj2 = obj;
sh_ptr<int> obj7;
obj7 = obj;

}
cout << " new object" << endl;

sh_ptr<float> obj3;
sh_ptr<double> obj4;
return 0;
}

- Sandeep Dutta December 29, 2012 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

template < typename T > class SP
{
private:
    T*    pData;       // pointer
    RC* reference; // Reference count

public:
    SP() : pData(0), reference(0) 
    {
        // Create a new reference 
        reference = new RC();
        // Increment the reference count
        reference->AddRef();
    }

    SP(T* pValue) : pData(pValue), reference(0)
    {
        // Create a new reference 
        reference = new RC();
        // Increment the reference count
        reference->AddRef();
    }

    SP(const SP<T>& sp) : pData(sp.pData), reference(sp.reference)
    {
        // Copy constructor
        // Copy the data and reference pointer
        // and increment the reference count
        reference->AddRef();
    }

    ~SP()
    {
        // Destructor
        // Decrement the reference count
        // if reference become zero delete the data
        if(reference->Release() == 0)
        {
            delete pData;
            delete reference;
        }
    }

    T& operator* ()
    {
        return *pData;
    }

    T* operator-> ()
    {
        return pData;
    }
    
    SP<T>& operator = (const SP<T>& sp)
    {
        // Assignment operator
        if (this != &sp) // Avoid self assignment
        {
            // Decrement the old reference count
            // if reference become zero delete the old data
            if(reference->Release() == 0)
            {
                delete pData;
                delete reference;
            }

            // Copy the data and reference pointer
            // and increment the reference count
            pData = sp.pData;
            reference = sp.reference;
            reference->AddRef();
        }
        return *this;
    }
};

- Nit January 25, 2014 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

wtf.. why is everyone making the refcount an pointer and new'ing it? What's wrong with an int?

- wtf May 09, 2014 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 votes

So that when you copy the shared pointer, the copies share the same refcount.

- mjb67 May 09, 2014 | Flag
Comment hidden because of low score. Click to expand.
0
of 0 vote

Here is a decent explanation on how to do that and why:

www_codeproject_com/Articles/15351/Implementing-a-simple-smart-pointer-in-c

(subs the _ with dots...)

- venera.varbanova April 05, 2015 | Flag Reply
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0
of 0 vote

Not thread safe.

- Anonymous November 16, 2015 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

#ifndef SHAREDPOINTER_H_
#define SHAREDPOINTER_H_


class RefCountMgr
{
public:
RefCountMgr():m_ref_count(0){}
void incrementRefCount(){ ++m_ref_count; }
void decrementRefCount() { --m_ref_count; }
int getRefCount() const {return m_ref_count;}
private:
int m_ref_count;
};

template<typename T>
class SharedPointer
{
public:
SharedPointer():m_t(0),m_ref_count_mgr(0){}
SharedPointer(T* t):m_t(t)
{
m_ref_count_mgr = new RefCountMgr();
m_ref_count_mgr->incrementRefCount();
}

~SharedPointer()
{
if(m_ref_count_mgr)
{
m_ref_count_mgr->decrementRefCount();
if(m_ref_count_mgr->getRefCount() <= 0)
{
delete m_t;
m_t = 0;
delete m_ref_count_mgr;
m_ref_count_mgr = 0;
}
}
}

SharedPointer(const SharedPointer& other)
{
m_t = other.m_t;
m_ref_count_mgr = other.m_ref_count_mgr;
m_ref_count_mgr->incrementRefCount();
}

SharedPointer& operator=(const SharedPointer& other)
{
if(this == &other)
return *this;
this->~SharedPointer();
m_t = other.m_t;
m_ref_count_mgr = other.m_ref_count_mgr;
m_ref_count_mgr->incrementRefCount();
return *this;
}

int refcount() const
{
if(m_ref_count_mgr)
return m_ref_count_mgr->getRefCount();
return 0;
}

T& operator*() const
{
return *m_t;
}

T* operator->() const
{
return m_t;
}

private:
RefCountMgr* m_ref_count_mgr;
T* m_t;
};




#endif /* SHAREDPOINTER_H_ */

- Murtuza July 23, 2017 | Flag Reply
Comment hidden because of low score. Click to expand.
0
of 0 vote

#ifndef SHAREDPOINTER_H_
#define SHAREDPOINTER_H_


class RefCountMgr
{
public:
	RefCountMgr():m_ref_count(0){}
	void incrementRefCount(){ ++m_ref_count; }
	void decrementRefCount() { --m_ref_count; }
	int getRefCount() const {return m_ref_count;}
private:
	int m_ref_count;
};

template<typename T>
class SharedPointer
{
public:
	SharedPointer():m_t(0),m_ref_count_mgr(0){}
	SharedPointer(T* t):m_t(t)
	{
		m_ref_count_mgr = new RefCountMgr();
		m_ref_count_mgr->incrementRefCount();
	}

	~SharedPointer()
	{
		if(m_ref_count_mgr)
		{
			m_ref_count_mgr->decrementRefCount();
			if(m_ref_count_mgr->getRefCount() <= 0)
			{
				delete m_t;
				m_t = 0;
				delete m_ref_count_mgr;
				m_ref_count_mgr = 0;
			}
		}
	}

	SharedPointer(const SharedPointer& other)
	{
		m_t = other.m_t;
		m_ref_count_mgr = other.m_ref_count_mgr;
		m_ref_count_mgr->incrementRefCount();
	}

	SharedPointer& operator=(const SharedPointer& other)
	{
		if(this == &other)
			return *this;
		this->~SharedPointer();
		m_t = other.m_t;
		m_ref_count_mgr = other.m_ref_count_mgr;
		m_ref_count_mgr->incrementRefCount();
		return *this;
	}

	int refcount() const
	{
		if(m_ref_count_mgr)
			return m_ref_count_mgr->getRefCount();
		return 0;
	}

	T& operator*() const
	{
		return *m_t;
	}

	T* operator->() const
	{
		return m_t;
	}

private:
	RefCountMgr* m_ref_count_mgr;
	T* m_t;
};




#endif /* SHAREDPOINTER_H_ */

- msharee9 July 23, 2017 | Flag Reply


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