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POGenerating Truly Random Numbers
 

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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/8278907/generating-random-numbers-effectively">Generating random numbers effectively</a> </p> </blockquote> <p>I need to generate <code>random numbers</code> in my <code>C++</code> application. I know from reading these two articles --</p> <p><a href="http://www.cprogramming.com/tutorial/random.html" rel="nofollow noreferrer">http://www.cprogramming.com/tutorial/random.html</a></p> <p><a href="https://stackoverflow.com/questions/3786389/write-a-c-function-that-generates-one-random-number-or-a-pair-of-random-numbers/3786809#3786809">write a c function that generates one random number, or a pair of random numbers, or a triplet of random numbers given the particular ranges</a></p> <p>-- that random numbers can be generated using <code>srand()</code> and <code>rand()</code> but in both cases the current time according to the <code>system clock</code> is used as a <code>seed</code>. But I read in the first article that <code>rand()</code> will create the same random numbers if the seed is the same. So if two different users ran my application at the same time then they would have the same random numbers. Which would be pointless because I need the random numbers to be unique for the most part. (I know they cant be truly 100% unique if they are generated randomly)</p> <p>So my question is can I create a random seed not based on system time and if so how, why does <code>rand()</code> produce the same numbers with the same seed and is there a way to make <code>rand()</code> produce different numbers with the same seed, or is there any other way to generate random numbers?</p>
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    1. USJohn Vulconshinz
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    1. COIt's not clear what your requirements are or what your platform is. For example, on most x86 platforms, you can get a time measurement to the billionth of a second (from the TSC) making the chance that two users will run your program at the same time effectively zero. (The exact answer to your question will depend a lot on your exact requirements and your platform.)
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      1. USDavid Schwartz
    2. COYou cam't generate truly random numbers without an external noise source - the best you can do is pseudorandom numbers.
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      1. USPaul R
    3. CO[Kolmogorov complexity](http://en.wikipedia.org/wiki/Kolmogorov_complexity) is not computable.
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