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copied!<p><em>First of all is this valid C++ or is it a microsoft extension?</em></p> <p>It is valid in C++, the relevant part of the standard is 5.3.4, with the first paragraph containing the grammar</p> <p><em>Is it guaranteed to initialize all the elements of the array?</em></p> <p>Yes. Paragraph 5.3.4/15 states that </p> <blockquote> <p>A new-expression that creates an object of type T initializes that object as follows:</p> <p>...</p> <ul> <li>If the new-initializer is of the form (), the item is value-initialized (8.5)</li> </ul> </blockquote> <p>where value initialized for POD means zero-initialize.</p> <p><em>Also, is there any difference if I do new int; or new int();? Does the latter guarantee to initialize the variable?</em></p> <p>Yes they are different. According with the quote above <code>new int()</code> will zero-initialize the integer. In a previous block of the same paragraph:</p> <blockquote> <p>If the new-initializer is omitted:</p> <ul> <li><p>If T is a (possibly cv-qualified) non-POD class type (or array thereof), the object is default-initialized (8.5). If T is a const-qualified type, the underlying class type shall have a user-declared default constructor.</p></li> <li><p>Otherwise, the object created has indeterminate value. If T is a const-qualified type, or a (possibly cv-qualified) POD class type (or array thereof) containing (directly or indirectly) a member of const-qualified type, the program is ill-formed;</p></li> </ul> </blockquote> <p>so <code>new int</code> will not initialize the memory.</p>

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