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    copied!<pre><code>MyClass&lt;2&gt; a(vector&lt;float&gt;()); </code></pre> <p>This is not a variable declaration. It is the declaration of a function named <code>a</code> that returns a <code>MyClass&lt;2&gt;</code> object and takes as an argument a "pointer to a function that takes no arguments and returns a <code>vector&lt;float&gt;</code>." Confusing? Yes. This is what is referred to as the "most vexing parse."</p> <p>You need extra parentheses:</p> <pre><code>MyClass&lt;2&gt; a((vector&lt;float&gt;())); ^ ^ </code></pre> <p>Or, you can use copy initialization:</p> <pre><code>MyClass&lt;2&gt; a = MyClass&lt;2&gt;(vector&lt;float&gt;()); </code></pre> <p>Or, since your constructor isn't <code>explicit</code>, you could use:</p> <pre><code>MyClass&lt;2&gt; a = vector&lt;float&gt;(); </code></pre> <p>(Though, unless you mean for <code>vector&lt;float&gt;</code> objects to be implicitly convertible to <code>MyClass&lt;N&gt;</code> objects, you probably want to make this constructor <code>explicit</code>.)</p> <hr> <p>A good compiler should warn you about this sort of thing. Visual C++ warns:</p> <blockquote> <p>warning C4930: '<code>MyClass&lt;x&gt; a(std::vector&lt;_Ty&gt; (__cdecl *)(void))</code>': prototyped function not called (was a variable definition intended?)</p> </blockquote> <p>Clang warns:</p> <blockquote> <p>warning: parentheses were disambiguated as a function declarator</p> <pre><code>MyClass&lt;2&gt; a(vector&lt;float&gt;()); ^~~~~~~~~~~~~~~~~ </code></pre> </blockquote>
 

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