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POCorrect way to initialize dynamic Array in C++
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  1. POCorrect way to initialize dynamic Array in C++
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    copied!<p>I'm currently working on a C++ project, where dynamic arrays often appear. I was wondering, what could be the correct way to initialize a dynamic array using the new-operator? A colleague of mine told me that it's a no-no to use new within the constructor, since a constructor is a construct that shouldn't be prone to errors or shouldn't fail at all, respectively. Now let's consider the following example: We have two classes, a more or less complex class State and a class StateContainer, which should be self-explained.</p> <pre><code>class State { private: unsigned smth; public: State(); State( unsigned s ); }; class StateContainer { private: unsigned long nStates; State *states; public: StateContainer(); StateContainer( unsigned long n ); virtual ~StateContainer(); }; StateContainer::StateContainer() { nStates = SOME_DEFINE_N_STATES; states = new State[nStates]; if ( !states ) { // Error handling } } StateContainer::StateContainer( unsigned long n ) { nStates = n; try { states = new State[nStates] } catch ( std::bad_alloc &amp;e ) { // Error handling } } StateContainer::~StateContainer() { if ( states ) { delete[] states; states = 0; } } </code></pre> <p>Now actually, I have two questions:</p> <p>1.) Is it ok, to call new within a constructor, or is it better to create an extra init()-Method for the State-Array and why?</p> <p>2.) Whats the best way to check if new succeeded: </p> <pre><code>if (!ptr) std::cerr &lt;&lt; "new failed." </code></pre> <p>or</p> <pre><code>try { /*new*/ } catch (std::bad_alloc) { /*handling*/ } </code></pre> <p>3.) Ok its three questions ;o) Under the hood, new does some sort of </p> <pre><code>ptr = (Struct *)malloc(N*sizeof(Struct)); </code></pre> <p>And then call the constructor, right?</p>
 

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