StackOverflow2013

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POC-style initialization lists in C++, structs, and class constructors
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copied!<p>I'm still on the road to enlightenment in C++, so bear with me...</p> <p>Suppose I have a struct:</p> <pre><code>struct MyThing { int a, b; }; </code></pre> <p>I fancy creating one using the c-style shorthand, Fig.1:</p> <pre><code>MyThing mt = { 1, 2 }; </code></pre> <p>Then suppose I decide to stick a method somewhere in my struct, and (being the kind of person that I am) I feel structs don't really suit methods, so turn it into a class:</p> <pre><code>class MyThing { public: int a, b; int sum() { return a + b; } }; </code></pre> <p>My Fig.1 still works fine - everything's hunky dory. Then I decide I'll eventually need a private method and member:</p> <pre><code>class MyThing { private: int c; void swap() { c = a; a = b; b = c; } public: int a, b; int sum() { return a + b; } }; </code></pre> <p>At this point, the c-style initialization list in Fig.1 fails to compile (in VS anyway) with "non-aggregates cannot be initialized with initializer list" - which is nicely explained here: <a href="http://msdn.microsoft.com/en-us/library/0s6730bb(v=vs.71).aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/0s6730bb(v=vs.71).aspx</a></p> <p>So I switch to:</p> <pre><code>class MyThing { private: void swap() { int c = a; a = b; b = c; } public: int a, b; MyThing (int _a, int _b) : a(_a), b(_b) {} int sum() { return a + b; } }; </code></pre> <p>then change Fig.1 to (Fig.2)</p> <pre><code>MyThing mt(1, 2); </code></pre> <p>Sooooo, after all that, my question is: is there any benefit of using c-style initialization lists (i.e. are they faster?) for creating things? Or would it do just as well in the first place to have:</p> <pre><code>struct MyThing { int a, b; MyThing(int _a, int _b) : a(_a), b(_b) {} }; </code></pre> <p>And use it as fig.2 from the beginning? Is there any performance hit at all (even if it's negligible)?</p> <p>Thank you!</p>

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