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copied!<h2>Memory Management</h2> <h3>Basics</h3> <ul> <li>Every 'use of' new must be matched by 'use of' delete</li> <li>Array new is different form normal new and has its own delete</li> </ul> <p>_</p> <pre><code> int* data1 = new int(5); delete data1; int* data2 = new int[5]; delete [] data2; </code></pre> <h3>Must Know</h3> <ul> <li>Exceptions</li> <li>RAII</li> <li>Rule of 4.</li> </ul> <p><a href="https://stackoverflow.com/questions/130117/throwing-exceptions-out-of-a-destructor/130123#130123">throwing exceptions out of a destructor</a><br> <a href="https://stackoverflow.com/questions/255612/c-dynamically-allocating-an-array-of-objects/255744#255744">Dynamically allocating an array of objects</a> <a href="https://stackoverflow.com/questions/1846144/1846409#1846409">Pattern name for create in constructor, delete in destructor (C++)</a></p> <h3>Best Practice</h3> <ul> <li>Never actually use RAW pointers.</li> <li>Always wrap pointers in Smart Pointers.</li> <li>Learn the different types of smart pointers and when to use each</li> </ul> <p><a href="https://stackoverflow.com/questions/94227/smart-pointers-or-who-owns-you-baby">Smart Pointers: Or who owns you baby?</a></p> <h3>Advanced:</h3> <ul> <li>Understanding Exception Guarantees</li> <li>Understanding the use of throw clause</li> </ul> <p><a href="https://stackoverflow.com/questions/106586/what-are-the-principles-guiding-your-exception-handling-policy/106749#106749">What are the principles guiding your exception handling policy?</a></p> <h2>Common ways to leak</h2> <h3>Basics</h3> <pre><code>// Every new is matched by a delete. for(int loop = 0;loop < 10;++loop) { data = new int(5); } delete data; // The problem is that every 'use of' new is not matched by a delete. // Here we allocate 10 integers but only release the last one. </code></pre> <h3>Must Know</h3> <pre><code>class MyArray { // Use RAII to manage the dynamic array in an exception safe manor. public: MyArray(int size) :data( new int[size]) {} ~MyArray() { delete [] data; } // PROBLEM: // Ignored the rule of 4. // The compiler will generate a copy constructor and assignment operator. // These default compiler generated methods just copy the pointer. This will // lead to double deletes on the memory. private: int* data; }; </code></pre> <h3>Best Practice</h3> <pre><code>// Understand what the properties of the smart pointers are: // std::vector<std::auto_ptr<int> > data; // Will not work. You can't put auto_ptr into a standard container. // This is because it uses move semantics not copy semantics. </code></pre> <h3>Advanced:</h3> <pre><code>// Gurantee that exceptions don't screw up your object: // class MyArray { // ... As Above: Plus void resize(int newSize) { delete [] data; data = new int[newSize]; // What happens if this new throws (because there is not enough memory)? // You have deleted the old data so the old data so it points at invalid memory. // The exception will leave the object in a completely invalid state } </code></pre>

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