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POExplicit Type Conversion and Multiple Simple Type Specifiers
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  1. POExplicit Type Conversion and Multiple Simple Type Specifiers
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    copied!<p>To value initialize an object of type <code>T</code>, one would do something along the lines of one of the following:</p> <pre><code>T x = T(); T x((T())); </code></pre> <p>My question concerns types specified by a combination of simple type specifiers, e.g., <code>unsigned int</code>:</p> <pre><code>unsigned int x = unsigned int(); unsigned int x((unsigned int())); </code></pre> <p>Visual C++ 2008 and Intel C++ Compiler 11.1 accept both of these without warnings; Comeau 4.3.10.1b2 and g++ 3.4.5 (which is, admittedly, not particularly recent) do not.</p> <p>According to the C++ standard (C++03 5.2.3/2, expr.type.conv):</p> <blockquote> <p>The expression <code>T()</code>, where <code>T</code> is a simple-type-specifier (7.1.5.2) for a non-array complete object type or the (possibly cv-qualified) <code>void</code> type, creates an rvalue of the specified type, which is value-initialized</p> </blockquote> <p>7.1.5.2 says, "the simple type specifiers are," and follows with a list that includes <code>unsigned</code> and <code>int</code>. </p> <p>Therefore, given that in 5.2.3/2, "simple-type-specifier" is singular, and <code>unsigned</code> and <code>int</code> are two type specifiers, are the examples above that use <code>unsigned int</code> invalid? (and, if so, the followup is, is it incorrect for Microsoft and Intel to support said expressions?)</p> <p>This question is more out of curiosity than anything else; for all of the types specified by a combination of multiple simple type specifiers, value initialization is equivalent to zero initialization. (This question was prompted by <a href="https://stackoverflow.com/questions/2143022/how-to-correctly-initialize-variable-of-template-type/2143038#2143038">comments in response to this answer to a question about initialization</a>).</p>
 

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