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    <pre><code>_Groups = (group **) new char[sizeof (group **) * NOMGRPS]; </code></pre> <p>This creates enough space for <code>NOMGRPS</code> group pointers and casts it to a pointer to a <code>group**</code>, presumably to be used as an array of pointers to objects of type <code>group</code> that are allocated elsewhere. This is (or more strictly speaking, was) a common idiom as <code>char</code> is almost always a single byte, so this says "Allocate <code>sizeof (group **) * NOMGRPS</code> bytes (enough bytes for <code>NOMGRPS</code> group pointers) and cast it to a pointer to a group pointer. So if <code>NOMGRPS</code> is 10, and you are on a 32 bit system, with 4 byte pointers, this allocates 40 bytes.</p> <pre><code>_Groups = new group*[sizeof (group **) * NOMGRPS]; </code></pre> <p>Here instead of saying you want 40 <code>char</code>s (i.e. bytes) you are saying you want 40 <code>group*</code>. So if <code>NOMGRPS</code> is 10, and you are on a 32 bit system, with 4 byte pointers, this allocates 40 * 4 or 160 bytes. This is almost certainly not what you want, but since it overallocates memory, it will likely work fine. Your instincts to make this change are right. Any time you cast in modern C++, you should consider it suspect. But you didn't quite go far enough.</p> <p>What you really want is this:</p> <pre><code>_Groups = new group*[NOMGRPS]; </code></pre> <p><code>new</code> knows the size of a <code>group*</code> and thus will allocate enough for <code>NOMGRPS</code> of them. This is more correct than the original version which used <code>new char</code>.</p>
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    1. USSteven Burnap
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    1. COHi,Steven thanks for your explanation.As I am still very new to c++ I still not really understand these.As for me I just know the basic concept of dynamic allocation. I like to understand thing in graphical view where I know you are not going to do that for me. So if i refering to this http://www.youtube.com/watch?v=i5gUlnrUqqQ is this graphical explanation can give me a better view?
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      1. USJaden Ng
    2. COBtw can i say: _Groups = new group*[NOMGRPS]; is wqual to _Groups = (group **) new char[sizeof (group **) * NOMGRPS]; ?
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    3. COYes, generally. It likely compiles to the same thing.
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