Using shared_ptr instead of raw pointers

This is a discussion on Using shared_ptr instead of raw pointers within the C++ Programming forums, part of the General Programming Boards category; Hi, I want to used shared_ptr here instead of raw pointers. How can the following code be changed to use ...

  1. #1
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    Using shared_ptr instead of raw pointers

    Hi,

    I want to used shared_ptr here instead of raw pointers. How can the following code be changed to use shared_ptr or shared_array?

    Code:
    #define  MAX_COLS 1000
    
    MyClass
    {
         private:
                    int	**m_value;
                    ...
    		...
         public:
            Myclass()
    	{
    		m_value = new int *[MAX_COLS];	
    		
    		for(int count = 0; count < MAX_COLS; count++ )
    		{
    			m_value[count] = NULL;
    		}	
    	}
    
            ~MyClass();
    	{
    		if(m_value)
    		{
    			for(int i = 0; i < MAX_COLS ; i++)
    			{
    				delete [](m_value[i]);
    			}
    			delete []m_value;
    			m_value = NULL;
    		}
    		
    	}
    
    	
    	void insert(index, int* data);
    	{
    		//do all the preliminary checks like bounds, null check
    		m_value[index] = data;
    		
    	}
    	
    
    	void processData()
    	{
    		for(int count = 0; count < MAX_COLS; count++  )
    		{
    			int *data  = m_value[count];
    			//Write the data to a file or do something with it
    		}
    		
    	}
    	
            //other members
    };

  2. #2
    C++ Witch laserlight's Avatar
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    std::tr1::shared_ptr is probably inappropriate here since you appear to be dealing with some kind of container of objects rather than a pointer to a single object.

    boost::shared_array might be appropriate since it looks like the insert member function does not make a copy. On the other hand, is this lack of a copy intentional, or is it an oversight? If it is intentional, perhaps a std::vector<boost::shared_array<int> > would be appropriate (or you could use a std::tr1::array<boost::shared_array<int>, MAX_COLS> instead). If not, perhaps a std::vector<std::vector<int> > would be better. Of course, you should change the insert member function's signature accordingly.

    If the indices can have many gaps in the sequence, perhaps a std::map would be better than a std::vector to store the shared_array or vector.
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  3. #3
    C++まいる!Cをこわせ! Elysia's Avatar
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    You seem to be using the old "C" way of 2D arrays. Are you use a std::vector< std::vector<int> > won't do?
    Consider also using const T instead of #define.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
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  4. #4
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    Thanks for ideas. The insert without copy is intentional.

    When do you use shared_ptr<> and when shared_array<>.

    what does these signify?

    boost::shared_ptr<int> smrtptr (new int[256]);
    and
    boost::shared_array<int> smrtarray (new int[256]);

  5. #5
    C++まいる!Cをこわせ! Elysia's Avatar
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    shared_ptr deletes with delete and shared_array deletes with delete[].
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.
    For information on how to enable C++11 on your compiler, look here.
    よく聞くがいい!私は天才だからね! ^_^

  6. #6
    Dae
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    shared_array also implements operator [] for element access, and I would assume has less overhead than an array of shared_ptr's.
    Warning: Have doubt in anything I post.

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