GSL Dirichlet Distribution in C++

Question

I am trying since quite some time to draw random variates from the gsl dirichlet distribution, but I cannot seem to make it work.

I have looked around for documentation/examples, but cannot find anything. Does anybody have any recommendations?

Basically, the function the gsl gives is:

void gsl_ran_dirichlet(const gsl_rng *r, size_t K, const double alpha[], double theta[])

Below you can find the code I am using. I can get the programm to return a random draw from the beta distribution, so it is compiling. But I am doing something (or probably) several things wrong for the dirichlet.

#include <iostream>
#include <stdlib.h>
#include <math.h>
#include "gsl/gsl_rng.h"
#include "gsl/gsl_randist.h"

using namespace std;

int main(int argc, const char *argv[])  {
    
    gsl_rng *gen = gsl_rng_alloc (gsl_rng_mt19937);             // allocate gsl_rng version of Mersenne twister
    gsl_rng_set(gen,(unsigned)time(NULL));                      // seed gsl_rng version of Mersenne twister
   //gsl_rng gen1;
    gsl_rng** gen1;
    gen1 = &gen;
    gsl_rng* gen2;
    gen2 = gen;

    double aBetaDist = 2; 
    double bBetaDist = 2; 
    double belateresult = gsl_ran_beta(gen,aBetaDist,bBetaDist);
    const size_t K = 3;
    const double alpha [3] = { 3, 3, 3}; 
    double theta[3];

void gsl_ran_dirichlet(const gsl_rng *r, size_t K, const double alpha[], double theta[]);
     gsl_ran_dirichlet(gen, K, alpha[], theta[]);

cout << "beta_value = " << gsl_ran_beta(gen,aBetaDist,bBetaDist) << endl;
cout << "beta_value1 = " << belateresult << endl;
cout << "alpha_value = " << alpha[2] << endl;

    gsl_rng_free(gen);
    return 0;
}

Thanks a lot for your help!