Free memory in c++ (armadillo)

Question

I want to free memory after using an object ('ii', in the following program) in c++:

#include <iostream>
#include <armadillo>

using namespace std;
using namespace arma;

int main()
{
    cx_mat ii(2,2,fill::eye);
    cout << ii <<endl;
    free (ii);
    return 0;
}

But after compiling, I encounter to the following error:

error: cannot convert ‘arma::cx_mat {aka arma::Mat<std::complex<double> >}’ to ‘void*’ for argument ‘1’ to ‘void free(void*)’

can any body guide me?

Answer 1

cx_mat ii(2,2,fill::eye);

That's allocated on the stack, you can't free it, it will be destroyed when your program exits the scope.

http://gribblelab.org/CBootcamp/7_Memory_Stack_vs_Heap.html

Answer 2

You can only free pointers holding an address returned by malloc , calloc or realloc . Nothing else. In particular, no matrices.

You also should not need to use free in C++, ever.

In your case, you do not need to do anything to free the memory, the destructor of the matrix will take care of that.

Answer 3

The reason you're getting the error you're getting is because you're not passing a pointer to the function.

However, free requires that you pass a pointer that has been returned by malloc , calloc , or realloc , otherwise undefined behavior occurs.

The memory of your object will be freed when your function returns, or exits.