Thread: Correct usage of malloc and free for 2D array

  1. #1
    Registered User
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    Jul 2005

    Correct usage of malloc and free for 2D array

    I have a program that requires to create and delete a 2D array of variable size, hence the dynamic usage. However I wish to ask a simple question about the correct or recommended usage. For example, where should I reallocate the memory, should I simply free up the memory and use another allocation of memory i.e. memory allocation double etc should be done once...

    or should be done in the loop

    double **ptrBeadArrayOld = NULL;
    ptrBeadArrayOld = (double **)malloc(BeadTotal * sizeof(double *));
    for (i = 0; i< BeadTotal; i++)

    or do I simply declare once?

    double **ptrBeadArrayOld = NULL;

    at the beginning of the program?? Thanks
    Last edited by disruptivetech; 10-20-2008 at 05:15 AM.

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    Are you asking about whether you should determine the final size of the array and then allocate once, versus filling up the array and expanding when necessary?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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