Thread: delete array of arrays

  1. #1
    Registered User
    Join Date
    Apr 2007

    delete array of arrays

    while(!fin.getline(info, 500).eof() )
    		arrayoffeat = new char * [10];
    		*arrayoffeat = new char[100];
    		        parseinputfromfile(info, arrayoffeat)
    		delete [] *arrayoffeat;
    		delete [] arrayoffeat;
    Hey there! I'm having trouble getting my memory to deallocate. pareinputfromfile function just goes through info, parses the information and loads up arrayoffeat. Then myclass is just an array of classes that sets the features into a private data structure. My problem is on outputting the array of characters to stdout. I'm getting garbage from the previous read in. So, its seems like I need to deallocate the memory after every rotation. I have put up my attempt at delete-ing the array of arrays, unfortantly it didn't work. I tried delete [] array[i]; well, it didn't like that.

    Any help would be greatly appriciated!

  2. #2
    Frequently Quite Prolix dwks's Avatar
    Join Date
    Apr 2005
    Your problem isn't in freeing that memory, it's in allocating it. To allocate a 2d array, you need something along these lines:
    int **array = new int*[SIZE];
    for(int i = 0; i < SIZE; i ++) {
        array[i] = new int[OTHERSIZE];
    Then you free it in reverse order:
    for(int i = 0; i < SIZE; i ++) {
        delete [] array[i];
    delete [] array;

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  3. #3
    Registered User
    Join Date
    Apr 2007
    Thanks! I was actually allocating the memory like that in my function, I guess I forgot about it while describing the problem. Thanks for the syntax on deleting array of arrays, I know it will come in useful! However, the problem I was having here wasn't deallocating memory, it was a \0 problem, *doh..

  4. #4
    Registered User
    Join Date
    Jan 2005
    In C++, you generally want to use a vector rather than a dynamic array, and a string rather than a dynamic array of chars (if it is meant to represent a string). Both will grow correctly and clean themselves up automatically.

    >> while(!fin.getline(info, 500).eof() )
    Why not while(!fin.getline(info, 500))? This checks for any failure. There is rarely a failure using getline, but checking for fail state is a more common idiom. Also, if your last line in the input file is not terminated with a newline, it won't be read in with your version but will be with mine.

  5. #5
    Registered User
    Join Date
    Apr 2007
    Thanks for the tips! You have sold me on using your form of getline. I'll have to look into vectors, I havn't used those before! As for strings, i'm actually amazed I forgot about those, thanks for the reminder! I'll have to practice with those too so as not to forget them in the future.

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