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POSafe Delete in C++
 

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  1. POSafe Delete in C++
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    <p>I have developed an array based implementation of a hashTable with several stock names, symbols, prices, and the like. I need to remove a stock from my array. I am told that using the delete operator is bad object oriented design. What is the good object oriented design for deletion?</p> <pre><code>bool hash::remove(char const * const symbol, stock &amp;s, int&amp; symbolHash, int&amp; hashIndex, int&amp; usedIndex) { symbolHash = this-&gt;hashStr( symbol ); // hash to try to reduce our search. hashIndex = symbolHash % maxSize; usedIndex = hashIndex; if ( hashTable[hashIndex].symbol != NULL &amp;&amp; strcmp( hashTable[hashIndex].symbol , symbol ) == 0 ) { delete hashTable[hashIndex].symbol; hashTable[hashIndex].symbol = NULL; return true; } for ( int myInt = 0; myInt &lt; maxSize; myInt++ ) { ++usedIndex %= maxSize; if ( hashTable[usedIndex].symbol != NULL &amp;&amp; strcmp( hashTable[usedIndex].symbol , symbol ) == 0 ) { delete hashTable[usedIndex].symbol; hashTable[usedIndex].symbol = NULL; return true; } } return false; } </code></pre> <p>Noticing that i have a stock &amp;s as a parameter, i can use it like this:</p> <pre><code>s = &amp;hashTable[usedIndex]; delete s.symbol; s.symbol = NULL; hashTable[usedIndex] = &amp;s; </code></pre> <p>This does work however, it results in a memory leaks. Even then, i am not sure if it is good object orinted design.</p> <p>here is my header, where stock and all that stuff is initialized and defined.</p> <p>//hash.h</p> <pre><code>private: friend class stock; int isAdded; // Will contain the added hash index. // Test for empty tables. // Can possibly make searches efficient. stock *hashTable; // the hashtable will hold all the stocks in an array }; </code></pre> <p>// hashtable ctor</p> <pre><code>hash::hash(int capacity) : isAdded(0), hashTable(new stock[capacity]) // allocate array with a fixed size { if ( capacity &lt; 1 ) exit(-1); maxSize = capacity; // We can initialize our attributes for the stock // to NULL, and test for that when searching. for ( int index = 0; index &lt; maxSize; index++ ) { hashTable[index].name = NULL; hashTable[index].sharePrice = NULL; hashTable[index].symbol = NULL; } } </code></pre> <p>// stock.h</p> <p>... friend class hashmap; </p> <pre><code>private: const static int maxSize; // holds the capacity of the hash table minus one date priceDate; // Object for the date class. Holds its attributes. char *symbol; char *name; int sharePrice; }; </code></pre> <p>My question is still just, how do i preform a safe remove?</p> <pre><code>s = &amp;hashTable[usedIndex]; delete s.symbol; s.symbol = NULL; hashTable[usedIndex] = &amp;s; </code></pre> <p>That seems to work, but results in memory leaks! How is this done safely?</p> <p>delete hashTable[usedIndex].symbol; hashTable[usedIndex].symbol = NULL; &lt;-- without doing this.</p> <p>The status of the slot in the array (empty, etc) should not be recorded in the stock instance. That's bad object oriented design. Instead, I need to store the status of an array slot in the array slot itself. </p> <p>How would i do that?</p>
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    1. USroalz
    1. USuser40120
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    1. COI am not sure about the delete operator, but having tons of const char* instead of strings and the thirty sixt reinvention of the wheel^H^H^H hashtable instead of a map is definetly a sign of bad design.
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      1. POSafe Delete in C++
      1. USGunther Piez
    2. COUsing delete has nothing to do with object oriented design, whoever told you that does not know what they are talking about. If you allocate memory on the heap you gave to delete it, period. These days we try to use idioms like RAII to encapsulate the process of managing heap memory, but at some point memory still needs to be freed.
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      1. POSafe Delete in C++
      1. USEd S.
    3. COThere is not enough information here to answer the question. The only fact that you manage to convey is: You have a class that can be used incorrectly because you give public access to internal parts of your structure. Thus is the bad OO design. The user of the class should not need to know or be able to manipulate the internal structure or modify an instance that would leave it in an inconsistant state.
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      1. POSafe Delete in C++
      1. USMartin York
 

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