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    <h2>struct inline initialization vs. inline constructors</h2> <p>Sometimes, we need in C++ a simple aggregation of data. The data being somewhat independant, protecting it through encapsulation would not be worth the effort.</p> <pre><code>// C-like code in C++ struct CRect { int x ; int y ; } ; void doSomething() { CRect r0 ; // uninitialized CRect r1 = { 25, 40 } ; // vulnerable to some silent struct reordering, // or adding a parameter } </code></pre> <p>; I see three problems with the code above:</p> <ul> <li>if the object is not specifically initialized, it won't be at initialized all</li> <li>if we echange x or y (for whatever reason), the default C initialization in doSomething() will now be wrong</li> <li>if we add a z member, and liked it to be "zero" by default, we would still need to change every inline initializing</li> </ul> <p>The code below will have the constructors inlined (if really useful), and thus, will have a zero cost (as the C code above):</p> <pre><code>// C++ struct CRect { CRect() : x(0), y(0) {} ; CRect(int X, int Y) : x(X), y(Y) {} ; int x ; int y ; } ; void doSomething() { CRect r0 ; CRect r1(25, 40) ; } </code></pre> <p>(The bonus is that we could add a operator== methods, but this bonus is out of topic, and so worth mentioning but not worth as an answer.)</p> <h2>Edit: C99 has named initialized</h2> <p>Adam Rosenfield made an interesting comment I find very interesting:</p> <p><em>C99 allows named initializers:</em> CRect r = { .x = 25, .y = 40 }</p> <p>This won't compile in C++. I guess this should be added to C++, if only for C-compatibiliy. Anyway, in C, it alleviates the problem mentioned in this answer.</p>
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    1. POC++ constructs replacing C constructs
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    1. COC99 allows named initializers: CRect r = { .x = 25, .y = 40 };
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    2. COInteresting point. This won't compile in C++ g++ ("error: expected primary-expression before ‘.’ token"), so this does not invalidate this whole post, but still a very good point worth knowing.
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    3. CONope, it doesn't compile with g++, but if you're compiling _pure_ C code, it works with gcc. I've tested it with gcc 3.4.4, but I'm sure it works in plenty of other versions of gcc as well.
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