Function that copies vector to another, already passing the destination address as parameter

Question

I want to make a function that copies a vector from double to another vector, allocating the new vector in the function that copies it.

That is the function:

void copiarvet(double *vet_origem, double *vet_destino, int n)
{

    vet_destino = malloc(n*sizeof(double));

    for(int i=0;i<n;i++)
        vet_destino[i]=vet_origem[i];
}

That way, it doesn’t work at all. I did it differently, making the function return a pointer to double, instead of void, and that way it worked.

I would like to understand, why, when trying to do this way, already passing the address as parameter is not working.