pointer/memory issue

acosgaya · #1 09-Feb-2007, 11:18

Hi, I have an issue with the following piece of code, in it I read a node from a binary file, and return it.

CPP / C++ / C Code:

Node* ArrayRTree::readNode(ifstream &in, int N_SIZE, int pos){
  Node* p = new Node(); 
  MYTYPE t; 

	for (int i = 0; i < m_maxDim; i++)
		p->m_pDims.push_back(t);		
	
	in.seekg(pos*N_SIZE);
	in.read(reinterpret_cast<char *>(&p->m_pDims[0]), sizeof(MYTYPE) * m_maxDim);
	in.read(reinterpret_cast<char *>(&p->m_child), sizeof(p->m_child));
	in.read(reinterpret_cast<char *>(&p->m_children), sizeof(p->m_children));		
	
	return p;
}
....

//I get the resulting value later in my code as:
 Node* p = new Node;   
 p = readNode(in, N_SIZE, 0);

this works fine, but I will call this operation many times, so I think doing this loop

CPP / C++ / C Code:

	for (int i = 0; i < m_maxDim; i++)
		p->m_pDims.push_back(t);

that many times, in the overall, costs me a lot of time, and also I am not sure if the "Node *p" inside the function ReadNode gets deleted after I return its contents, or maybe I am creating a new one every time I call the function, and the previous one is still in memory, causing waste of it. is this really happening?

So I was thinking, maybe instead of returning the node, better to pass it to the function (do the for loop outside), and it just gets rewritten every time I use it. The problem is that I tried it, but it didn't work, and as I am storing those read values somewhere else, it just becomes a mess, and only keeps the last value that was read.

this was my idea, that didn't work:

CPP / C++ / C Code:

void ArrayRTree::readNode(Node *p, ifstream &in, int N_SIZE, int pos){

	in.seekg(pos*N_SIZE);
	in.read(reinterpret_cast<char *>(&p->m_pDims[0]), sizeof(MYTYPE) * m_maxDim);
	in.read(reinterpret_cast<char *>(&p->m_child), sizeof(p->m_child));
	in.read(reinterpret_cast<char *>(&p->m_children), sizeof(p->m_children));			
			
}

...
// later on
 Node* p = new Node;   
 readNode(p, in, N_SIZE, 0); 

 // but p doesn't seem to get the right value

I guess it has to do with some pointer management, but not sure how to fix it.

I'd appreciate any insight and help with it.

Thanks

davekw7x · #2 09-Feb-2007, 12:50

Since the class for which m_pDims is an object has a push_back() function and overloaded [], maybe it has resize(). (Like a std::vector, for example). If it does, then maybe the loop could be replaced by

CPP / C++ / C Code:

    p->m_pDims.resize(m_maxDim);

(I am assuming that the vector has size = 0 when this function is invoked, otherwise the resize argument would be p->m_pDims.size() + m_maxDim, since your loop appends that m_maxDim elements to whatever the present vector is.)

(I'm assuming that m_maxDim is not constant for a given object of this class; otherwise you would have fixed the size in the constructor, right?)

(I'm also assuming that you really need a vector, since if you aren't actually using m_pDims as a vector ---that is, you are always accessing it with [] notation rather than pushing and popping and you always know its size--- then you would have made it an array rather than a vector, right?)

Regards,

Dave

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pointer/memory issue

Re: pointer/memory issue