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POclasses before main and design issues in C++
 

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    <p><strong>PART 1:</strong> I have a very odd situation, where in, I have to get the constructors of several classes called before main() or as soon as it enters main(). There's another sub-system which needs that data ASAP main() of this sub-system starts and more stuff, which make this concept appear more useful.</p> <p>I have two approaches here:</p> <ol> <li><p>Use a global object before main().</p></li> <li><p>use a static class definition, in the first line of main().</p></li> </ol> <p>One more idea, is(since I use gcc) is to use the <code>attribute __constructor__</code> gcc reserved function.</p> <p>What would you suggest?</p> <p><strong>PART 2:</strong> To add further to the issue, I need to decouple the development of those classes.(This is more of a code base design issue.)</p> <p>That is, if someone is writing a <strong>classA</strong> and someone else is writing <strong>classB</strong>, then we would have two separate files with <strong>classA</strong> and <strong>classB</strong>, defined and <em>calling their own constructors within their files/modules</em>.</p> <p>This is a sample code, that illustrates my idea:</p> <pre><code>class Init_myclass { public: Init_myclass(): myvar(10) { std::cout &lt;&lt; __PRETTY_FUNCTION__ &lt;&lt; ":" &lt;&lt; myvar &lt;&lt; std::endl; }; private: int myvar; }; static Init_myclass TestInit; //Initializing object prior to main int main () { std::cout &lt;&lt; __PRETTY_FUNCTION__ &lt;&lt; std::endl; //Use the data populated by the Init_myclass constructor return 0; } </code></pre> <p>In the above code, replace <strong>Init_myclass</strong> with 100s of class definitions like <strong>classA,classB</strong>,etc. </p> <p>The other approach is <em>using a single constructor in a file to call multiple classes constructors defined in other files</em>, from within.</p> <p>Here's the sample code that might help you understand my idea:</p> <pre><code>class InitializeOne { public: InitializeOne(): myvar(10) { std::cout &lt;&lt; __PRETTY_FUNCTION__ &lt;&lt; ":" &lt;&lt; myvar &lt;&lt; std::endl; A bunch of constructors of other classes here(); classA(); classB(); .... }; private: int myvar; }; int main() { static InitializeOne TestInit;//Object after main ... //functions depending on data populated by Initialize constructor } </code></pre> <p>The initialization order of the classes doesn't matter, but they have to be initialized before main or as soon as entering main.</p> <p>Which design is more preferable and why?</p> <p>I hope, I am making my question understandable. If not, do let me know, what information I have missed out or oversimplified/complicated or such.</p> <p>Thank You for your responses and time.</p>
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    1. COIMHO, there's s.th wrong with the design of your subsystem (which you don't elaborate further), if it needs to rely on (at least so many) singletons.
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    2. COThat subsystem is a 3rd party DB engine, which in turn is monitored by the other processes for relevant data. I agree, that its really a bad design(evolved out of a mud ball), but that's how it gotta be, to be approved into the codebase. :(
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    3. COOK, I already guessed s.th. like this. In this case you should provide just one singleton class, that calls all the necessary constructors on it's own instantiation (constructor). In other words: Make a singleton class, that instantiates members for all the classes that need to be instantiated on `main()` entry, and access your singleton instance once.
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