memcpy problem

This is a discussion on memcpy problem within the C++ Programming forums, part of the General Programming Boards category; I am trying to create a function to add a new entry to an array of pointers, for example: Assuming ...

  1. #1
    Registered User
    Join Date
    May 2004
    Posts
    19

    memcpy problem

    I am trying to create a function to add a new entry to an array of pointers, for example:

    Assuming i have my CameraCircuit structure set like this:

    Code:
    struct CameraCircuit
    {
    	GLdouble **locations_list;
    	GLint locations_list_size;
    };
    And it is already initialized so that i have:

    cameras.locations_list = { {1,2,3}, {4,5,6}}
    cameras.locations_list_size = 2;

    And then i want to add a new camera, to the end of the list so that its location is:

    {10,11,12}

    My function should change the variable (redimensionate the memory etc...) so that after i call the function i have:

    cameras.locations_list = { {1,2,3}, {4,5,6},{10,11,12}}
    cameras.locations_list_size = 3;

    I have this, the problem is that although it seems to set up the memory correctly, it doesent seem to copy the date at all.
    The idea behind this is to create a buffer with the new size, copy the old data to it, then delete the old data and set the pointer to the new data. It may be quite simple, but i really have no idea how to do it. A little help would be greatlly apreciated. Thanks.

    Code:
    void CreateCamera(CameraCircuit *cameras, const double *location)
    {
    	int locationsize = sizeof(double) * 3;
    	int oldsize = cameras->locations_list_size;
    	cameras->locations_list_size++;
    	int newsize = cameras->locations_list_size;
    	double **newbuffer = new double*[newsize];
    	for(int i = 0; i < newsize; i++)
    		newbuffer[i] = new double[3];
    	memset(newbuffer, 0, locationsize * newsize);
    	memcpy(newbuffer, cameras->locations_list, locationsize * oldsize);
    	for(int i = 0; i < oldsize; i++)
    		delete [] cameras->locations_list[i];
    	delete [] cameras->locations_list;
    	cameras->locations_list = newbuffer;
    	for(int i = 0; i < 3; i++)
    		cameras->locations_list[cameras->locations_list_size - 1][i] = location[i];*/
    }

  2. #2
    Registered User
    Join Date
    May 2003
    Posts
    161
    The problem is that you're using memcpy() as if you had a two dimensional array when what you really have is an array of pointers to arrays.

    You'll have to loop through your array and copy them over manually. Or (and this is the better option), just copy the pointers over.

    Here is the modified code:
    Code:
    void CreateCamera(CameraCircuit *cameras, const double *location)
    {
    	int oldsize = cameras->locations_list_size;
    	cameras->locations_list_size++;
    	int newsize = cameras->locations_list_size;
    	double **newbuffer = new double*[newsize];
            // no need to delete and reallocate each location-- just copy
            // the pointers over
    	for(int i = 0; i < oldsize; i++)
    		newbuffer[i] = cameras->locations_list[i];
    	delete [] cameras->locations_list;
    	cameras->locations_list = newbuffer;
            // add the new location to the end of the new array
            newbuffer[newsize-1] = new double[3];
    	for(int i = 0; i < 3; i++)
    		cameras->locations_list[newsize - 1][i] = location[i];*/
    }
    Hope that helps.

    -tf

  3. #3
    Registered User
    Join Date
    May 2004
    Posts
    19
    worked! thanks a lot

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Memory problem with Borland C 3.1
    By AZ1699 in forum C Programming
    Replies: 16
    Last Post: 11-16-2007, 11:22 AM
  2. Someone having same problem with Code Block?
    By ofayto in forum C++ Programming
    Replies: 1
    Last Post: 07-12-2007, 09:38 AM
  3. A question related to strcmp
    By meili100 in forum C++ Programming
    Replies: 6
    Last Post: 07-07-2007, 03:51 PM
  4. WS_POPUP, continuation of old problem
    By blurrymadness in forum Windows Programming
    Replies: 1
    Last Post: 04-20-2007, 07:54 PM
  5. Replies: 14
    Last Post: 06-28-2006, 02:58 AM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21