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POC++ construction: "MyClass c" is bad, "MyClass c = MyClass()" is slow, I want "MyClass c()"
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  1. POC++ construction: "MyClass c" is bad, "MyClass c = MyClass()" is slow, I want "MyClass c()"
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    copied!<p>Here's some code:</p> <pre><code>class MyClass { public: int y; }; int main() { MyClass item1; MyClass item2 = MyClass(); } </code></pre> <p>When I run this, I receive the following values:</p> <pre><code>item1.y == [garbage] item2.y == 0 </code></pre> <p>Which, well, surprises me.</p> <p>I expected item1 to be default-constructed and item2 to be copy-constructed off an anonymous default-constructed instance of MyClass, resulting in both equaling 0 (since default-constructors initialize members to default values). Examining the assembly:</p> <pre><code>//MyClass item1; //MyClass item2 = MyClass(); xor eax,eax mov dword ptr [ebp-128h],eax mov ecx,dword ptr [ebp-128h] mov dword ptr [item2],ecx </code></pre> <p>Shows item2 being constructed by writing a '0' value somewhere temporary and then copying it into item2, as expected. However, there's NO assembly for item1. </p> <p>So, the program has memory for item1 in the stack but it never <em>constructs</em> item1.</p> <p>I can appreciate wanting that behavior for speed purposes, but I want the best of both worlds! I want to know item1.y == 0 (it gets constructed), but I don't want to waste time on default-construct-anonymous-instance-then-copy-construct like item2 does. </p> <p>Frustratingly, I can't force a default-construct by saying <code>MyClass item1();</code> since that is interpreted as a function prototype. </p> <p>So... if I want to use the default constructor on item1 without also copy-constructing, how the heck do I do that?</p> <p>Side-note: it looks like if I declare a constructor for MyClass, item1 is constructed as usual. So this behavior only applies to compiler-generated constructors.</p>
 

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