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POC++ Hash Table using chaining, remove method
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  1. POC++ Hash Table using chaining, remove method
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    copied!<p>I'm implementing a Hash Table in C++ using chaining. The code builds with no errors and the table constucts fine using the insert method. However, when I call the remove method I receive the following error:</p> <p>Unhandled exception at 0x00c53be9 in HashTable.exe: 0xC0000005: Access violation reading location 0x00000000.</p> <p>Hash Entry Code:</p> <pre><code>#include &lt;string&gt; #include &lt;vector&gt; template &lt;class T&gt; class HashEntry { private: int key; //lookup key T value; //hash data HashEntry&lt;T&gt; *next; public: HashEntry(int key, T value); HashEntry(); int&amp; getKey(); T&amp; getValue(); void setValue(T value); HashEntry&lt;T&gt;* getNext(); void setNext(HashEntry *next); bool operator == (HashEntry&amp; rhs); bool operator != (HashEntry&amp; rhs); HashEntry&lt;T&gt;&amp; operator = (HashEntry&amp; rhs); }; template &lt;class T&gt; HashEntry&lt;T&gt;::HashEntry(int key, T value) { this-&gt;key = key; this-&gt;value = value; this-&gt;next= nullptr; } template &lt;class T&gt; HashEntry&lt;T&gt;::HashEntry() { this-&gt;key = 0; this-&gt;next= nullptr; } template &lt;class T&gt; int&amp; HashEntry&lt;T&gt;::getKey() { return key; } template &lt;class T&gt; T&amp; HashEntry&lt;T&gt;::getValue() { return value; } template &lt;class T&gt; void HashEntry&lt;T&gt;::setValue(T value) { this-&gt;value = value; } template &lt;class T&gt; HashEntry&lt;T&gt;* HashEntry&lt;T&gt;::getNext() { return next; } template &lt;class T&gt; void HashEntry&lt;T&gt;::setNext (HashEntry *next) { this-&gt;next = next; } template &lt;class T&gt; bool HashEntry&lt;T&gt;::operator == (HashEntry&amp; rhs) { return ((this-&gt;getKey() == rhs.getKey()) &amp;&amp; (this-&gt;getValue() == rhs.getValue())); } template &lt;class T&gt; bool HashEntry&lt;T&gt;::operator != (HashEntry&amp; rhs) { return ((this-&gt;getKey() != rhs.getKey()) &amp;&amp; (this-&gt;getValue() != rhs.getValue())); } template &lt;class T&gt; HashEntry&lt;T&gt;&amp; HashEntry&lt;T&gt;::operator = (HashEntry&amp; rhs) { this-&gt;key = rhs.getKey(); this-&gt;value = rhs.getValue(); this-&gt;next = rhs.getNext(); return *this; } </code></pre> <p>Hash Table code:</p> <pre><code>template &lt;class T&gt; class HashTable { private: std::vector&lt;HashEntry&lt;T&gt;&gt; table; static const int DEFAULT_TABLE_SIZE = 128; int TABLE_SIZE; public: HashTable(); void insert(int key, T value); void remove(int key); void get(int key); ~HashTable(); }; template &lt;class T&gt; HashTable&lt;T&gt;::HashTable() { TABLE_SIZE = DEFAULT_TABLE_SIZE; table.resize(TABLE_SIZE); } </code></pre> <p>Remove Method Code:</p> <pre><code>template &lt;class T&gt; void HashTable&lt;T&gt;::remove(int key) { int hashFunc = (key % TABLE_SIZE); if (table[hashFunc] != HashEntry&lt;T&gt;()) { HashEntry&lt;T&gt; prevEntry = HashEntry&lt;T&gt;(); HashEntry&lt;T&gt; entry = table[hashFunc]; while (entry.getNext() != nullptr &amp;&amp; entry.getKey() != key) { prevEntry = entry; entry = *entry.getNext(); } if (entry.getKey() == key) { if (prevEntry == HashEntry&lt;T&gt;()) { HashEntry&lt;T&gt; nextEntry = *entry.getNext(); //Where the exception is thrown entry = HashEntry&lt;T&gt;(); table[hashFunc] = nextEntry; } else { HashEntry&lt;T&gt; *next = entry.getNext(); entry = HashEntry&lt;T&gt;(); prevEntry.setNext(next); } } } } </code></pre>
 

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