How to manage a series of gsl_vector

Question

I've got a homework to write an iterative solver(L-BFGS) which needs to save 10 vectors. And update with the latest vector while remove the oldest. I'm using gsl_vector for all other computations, thus I would like to save them directly.

Using vector and vector.push_back and vector.erase was my first thought. But I find it difficult to use it because gsl_vector objects are declared by pointers. If I push_back the pointer, I still have to keep the pointer variable which has no difference with I manually manage the 10 saved variables.

It is appreciated if you could provide some directions on how to managed such.

A short example code:

vector<gsl_vector*> storage(10);

gsl_vector* v = gsl_vector_alloc(100);
gsl_vector_set_zero(v); 

storage.push_back(v);
if (storage.size()>10){
    storage.erase(storage.begin());
}

gsl_vector_set_all(v, 1); //Could be any other computation

storage.push_back(v);
if (storage.size()>10){
    storage.erase(storage.begin());
}

What I want is to save the two different gsl_vector into std::vector. However, due to the fact gsl_vector is an pointer, eventually I have a vector of the same pointer thus no value is stored. If I create 10 pointer objects, then the std::vector became useless, I will be still managing the storage by the 10 pointer variables.

Answer 1

I do not understand why you need to keep the pointer variable, the gsl_vector is heap allocated, and you do not need to keep a pointer to it outside the std::vector to keep it alive. What I would suggest is to use a smart pointer with custom deleter, to avoid leaking resources:

#include <vector>
#include <memory>
#include <gsl/gsl_vector.h>

struct gls_vector_deleter {
    void operator()(gsl_vector* v) {
        gsl_vector_free(v);
    }
};

int main()
{

    using gsl_vector_ptr = std::unique_ptr<gsl_vector, gls_vector_deleter>;

    std::vector<gsl_vector_ptr> storage(10);

    gsl_vector_ptr v{ gsl_vector_alloc(100) };
    gsl_vector_set_zero(v.get());

    storage.push_back(std::move(v));
    if (storage.size() > 10) {
        storage.erase(storage.begin());
    }

    //can't use v anymore, lost ownership, use the one stored in vector or a new one
    gsl_vector_ptr v2{ gsl_vector_alloc(100) };
    gsl_vector_set_all(v2.get(), 1);
    storage.push_back(std::move(v2));

    if (storage.size() > 10) {
        storage.erase(storage.begin());
    }
}