C++ Generating random numbers in functions

For a project that I am working on I need to generate a vector of random numbers within a function. The problem is that I end up generating the same vector of numbers each time. I have this example that reproduces my problem:

#include <iostream>
#include <random>

std::vector<double> generate(std::default_random_engine generator, double mean, double sigma, int n)
{
    std::vector<double> generated(n,0);
    std::normal_distribution<double> distribution(mean,sigma);
    for (int i = 0;i<n;i++)
        generated[i] = distribution(generator);
    return generated;
}
std::vector<double> generate(double mean, double sigma, int n)
{
    std::vector<double> generated(n,0);
    std::default_random_engine generator;
    std::normal_distribution<double> distribution(mean,sigma);
    for (int i = 0;i<n;i++)
        generated[i] = distribution(generator);
    return generated;
}

int main(int argc, char** argv)
{
    // Read inputs
    int nrolls = 20;  // number of experiments
    int ntimes = 50;
    double mean = 100;
    double sigma = 4;
    bool useFunction(false);
    if (argc>1)
        useFunction=true;

    // crates series
    std::vector< std::vector<double> > results(ntimes,std::vector<double>());
    std::default_random_engine generator;
    for (int i = 0;i<ntimes/4;i++){
        std::vector<double> generated(nrolls,0);
        std::normal_distribution<double> distribution(mean,sigma);
        for (int i = 0;i<nrolls;i++)
            generated[i] = distribution(generator);
        results[i] = generated;
    }
    for (int i = ntimes/4;i<ntimes/2;i++)
        results[i] = generate(generator,mean,sigma,nrolls);
    for (int i = ntimes/2;i<3*ntimes/4;i++){
        std::vector<double> generated(nrolls,0);
        std::normal_distribution<double> distribution(mean,sigma);
        for (int i = 0;i<nrolls;i++)
            generated[i] = distribution(generator);
        results[i] = generated;
    }
    for (int i = 3*ntimes/4;i<ntimes;i++)
        results[i] = generate(mean,sigma,nrolls);
     //

    // Display all random numbers
    for (int i = 0;i<ntimes;i++){
        std::cout<<i;
        for (int j = 0;j<nrolls;j++)
            std::cout<<" "<<results[i][j];
        std::cout<<std::endl;
    }

    // Check number of equal results
    int n_equal(0);
    int n_total(0);
    for (int i=0;i<ntimes;i++){
        for (int k = 0;k<nrolls;k++){
            for (int j=i+1;j<ntimes;j++){
                n_total++;
                if (results[i][k] == results[j][k])
                    n_equal++;
            }
        }
    }
    std::cout<<n_equal<<"/"<<n_total<<std::endl;

    // Exit
    return 0;
}

I have tried to solve it by passing the generator to the function where the array of random numbers is generated but apparently, it does not work either. Can somebody give me a hint on how should I do it to get different arrays each time i call the generate function?

Thank you very much.