Question

I want to generate eight bit (uint8_t) random numbers so that I exclude a set of well known numbers which have already been specified. Basically numbers from 0x00 – 0xFF but I have certain numbers within that range that I do not want to appear.

I am thinking of just populating a vector with the numbers allowed and pick a (pseudo) random index and use that one.

I suspect their may be serious short comings with this so looking for leads/advice. The solution need not be rocket science grade but just simple enough to “appear” random 🙂

EDIT: I do not want to use external libraries like boost as I am working on ARM embedded solution

EDIT: I do not have support for C++11

Answer 1

#include <iostream>
#include <algorithm>
#include <ctime>

int main()
{
    srand(time(0));
    int exclude [] = {4,6,2,1};
    // Test Values for Exclude
    std::sort(exclude, exclude + 4);

    int test = 0;
    for (int i = 0; i < 50; ++i)
    {
        // While we haven't gotten a valid val.
        while ( std::binary_search(exclude, exclude + 4, test = (rand() % 256))); 
        std::cout << test << std::endl; // Print matched value
    }
    return 0;
}

I think this will work a little bit faster than @IceCoder’s solution.