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copied!<p>Is there a reason you're not just using <code>rand()</code>, which is part of the C++ standard library? The function you refer to is part of the Single UNIX Specification, but is probably not portable...</p> <p>The reason you're getting the same value over and over is because you're not seeding the random number generator, so it behaves deterministically. Use <code>srand()</code> or <code>srand48()</code> if you're OK with the UNIX-specific functions and need the 48-bit precision. <strong>Only call it once</strong> at the beginning of your program, and pass it <code>time(NULL)</code>. Don't worry about using <code>time()</code>, since you're only calling this function once, you don't need to worry about always getting the same time value.</p> <p>You may also want to refer to this page about how to take the return value from <code>rand()</code> and scale it to the range you want effectively:</p> <p><a href="http://members.cox.net/deleyd/random/crandom.html" rel="nofollow" title="USING THE C OR C++ rand() FUNCTION">USING THE C OR C++ rand() FUNCTION</a></p> <hr> <p>EDIT: Go back and read the docs for <code>erand48</code> again. You'll notice it returns a double in the range [0, 1). You're putting that in a long, which is probably why you're always seeing zero (the value is truncated to an integer). I also think that it's probably updating the values of the <code>unsigned long</code> array for you with the current number in the sequence -- you provide the storage, it uses it to "keep track" of the sequence.</p> <p>Try:</p> <pre><code>unsigned short xsubi[3] = { 0, 1, 27 }; for (int i = 0; i < 10; ++i) { double value = erand48(xsubi); printf("%f\n", value); } </code></pre>

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