Prime number seive help?

[Pkmnmster]

I saw that there has been a TON of messages regarding this on here recently and I hope that this isn't going to hit the cap on the "Sieve of E." (I can't spell that guys name... :/ )

[naraku9333]

Heres an example using a vector of bools

#include <vector>
#include<iostream>
#include <cmath>
#include <iomanip>
 
int main()
{
    const std::size_t size = 100000;
    
    //initialize all numbers as "prime"
    std::vector<bool> primes(size, true);
    
    int sq = std::sqrt(size);
    for(int i = 2; i < sq; ++i)
    {
        if(primes[i])//if i is prime set all multiples to false (not prime)
        {
            for(int j = 2; j*i < size; ++j )
            {
                if(primes[i * j])
                    primes[j * i] = false;
            }
        }
    }
    //output in pretty columns
    int c = 1;//counter used for formatting
    for(int i = 1; i < size; ++i)
    {
        if(primes[i])
        {
            std::cout << std::setw(7) << i << " ";
            if(c % 14 == 0)
                std::cout << std::endl;
            ++c;
        }
    }
}

[cire]

Does this look ok?

Given: vector<int>& primes

set<int>::iterator m = primes.begin(); definitely does not look ok.

[Pkmnmster]

Here is the updated code. Any suggestions?

void
findVectorPrimes(int num, vector<int>& v, set<int>& primes)
{
  
  int squareRoot = sqrt(num);
  vector<int>::iterator m = v.begin();
  while (*m <= squareRoot)
    {
      for (size_t k = *m; k <= num; k++)
	  {
	    
		vector<int>::iterator j = v.at((*m) * k);
	    v.erase(j);
		
	  }
      
      ++m;
      
    }	
	primes.clear();
	copy(v.being(), v.end(), primes.begin());
}

[ne555]

The set does not let you modify the elements because you could break the order.
Use http://www.cplusplus.com/reference/set/set/insert/ instead.

Do a desk test (also, make your code compilable)

[cire]

It's hard to relate the code you supply with the subject of the thread since you definitely do not seem to be implementing a sieve. Is it your intent for v to represent the sieve? If it is, what do you think you're accomplishing by erasing elements?

I would worry more about getting the sieve right than I would about how to fill a set with the sieve results.

[edit: And why don't you move this out of the unix/linux forum to one where it's on topic?]

[Pkmnmster]

Sorry for the delay. I got it figured out. Thanks. ;3