Oct 28, 2015 · Like rand(), rand_r() returns a pseudo-random integer in the range [0, RAND_MAX]. The seedp argument is a pointer to an unsigned int that is used to store state between calls. If rand_r() is called with the same initial value for the integer pointed to by seedp, and that value is not modified between calls, then the same pseudo-random sequence ...

Jul 25, 2013 · You need to seed the random number generator, from man 3 rand. If no seed value is provided, the rand() function is automatically seeded with a value of 1. and. The srand() function sets its argument as the seed for a new sequence of …

Sep 27, 2011 · The c++ rand() function gives you a number from 0 to RAND_MAX (a constant defined in <cstdlib>), which is at least 32767. (from the c++ documentation) The modulus (%) operator gives the remainder after dividing. When you use it with rand() you are using it to set an upper limit (n) on what the random number can be.

Oct 24, 2013 · The equivalent half-open range is [0, n), and rand() % n == rand() % (n-0) + 0. So the lesson is: don't confuse half-open ranges for closed ranges. A second lesson is that this shows another way in which <random> is easier to use than rand() and manually computing your own distributions.

Jul 30, 2009 · Related: How to generate a random int in C?. Here is my answer there, which contains the definition for my int utils_rand(int min, int max) func, which returns a random number using rand() which is in the specific range from min to …

Jul 28, 2009 · rand() This function returns a random number between 0 and RAND_MAX, which is a macro that is defined as a rather large integer. Step 4. Get your random number into the range you want. The general formula for doing so is this: int random_number = rand() % range + min;

No, because RAND_MAX is typically expanded to MAX_INT. So adding one (apparently) puts it at MIN_INT (although it should be undefined behavior as I'm told), hence the reversal of sign. To get what you want you will need to move the +1 outside the computation: r = ((double) rand() / (RAND_MAX)) + 1;

Nov 17, 2013 · Using the remainder to clamp outputs from rand to a specified range will usually cause bias in the results. To be specific, if the range of the generator (RAND_MAX in the case of C or C++) isn't a multiple of the range you're clamping to, …

Aug 23, 2010 · Now, if you are interested on the reasons why the above is true, here are the gory details on how rand() works: rand() is what's called a "linear congruential generator." This means that it employs an equation of the form: x n+1 = (*a****x n + ***b*) mod m. where x n is the n th random number, and a and b are some predetermined integers.

Mar 14, 2013 · From the rand man page: The function rand() is not reentrant or thread-safe, since it uses hidden state that is modified on each call. So don't use it with threaded code. Use rand_r (or drand48_r if you're on linux/glibc). Seed each RNG with a different value (you could seed a first RNG in the main thread to produce random seeds for the ones in ...