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POHow often should I reseed in C++?
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  1. POHow often should I reseed in C++?
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    copied!<p>I just wonder if it is enough to seed the random number generator only once at the beginning of a program. I write functions which uses random numbers. I never seed the rand() generator within the function, but rather leave calling srand() on main entry. E.g. my program may look like:</p> <pre><code>void func1() { std::cout &lt;&lt; "This is func1 " &lt;&lt; std::rand() &lt;&lt; std::endl; } void func2() { std::cout &lt;&lt; "This is func2 " &lt;&lt; std::rand() &lt;&lt; std::endl; } int main() { std::srand(std::time(NULL)); func1(); func2(); return 0; } </code></pre> <p>By doing so, I can easily switch off seeding from the main entry. It comes useful when debugging a program - the results are kept the same every time I run the program without seeding. Sometimes, if a problem occurs due to some random number, it may just disappear if a different set of random numbers is to be generated, so I'd prefer such a simple mechanism to switch off seeding.</p> <p>However, I noticed in C++11's new random utility set, the random number generator has to be instantiated before using. (e.g. default_random_engine). And every time a generator has to be seeded separately. I wonder if it is actually encouraged to reseed the generator whenever a new generator is needed. I know I could create a global random generator and seed it only once as before, but I don't really like the idea of using global variables at all. Otherwise, if I create a local random number generator, I sort of lose the ability to globally switch off seeding for debugging or whatever purpose.</p> <p>I'm excited to learn the new features in C++11, but sometimes it's just very confusing. Can anyone let me know if I got anything wrong with the new random generators? Or what might be the best practice in C++11?</p>
 

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