How to share common memory in armadillo?

问题

In armadillo, the advanced constructor provide the way to share memory like

mat B(10,10);

mat A(B.memptr(),2,50,false, true);

but in c++ program about class, one should first declare variables in head file,like

mat A,B;

and realize other things in cpp file.

So, anyone can tell me how to share memory between mat A and mat B in cpp file with the declaration of mat A and B in head file?

回答1:

You can declare the B matrix as reference the A matrix when declaring your class. For example:

class foo
   {
   public:

   mat  A;
   mat& B;  // alias of A

   foo()
     : B(A)  // need to initialize the reference as part of the constructor
     {
     A.zeros(4,5);
     A(1,1) = 1;
     B(2,2) = 2;

     A.print("A:");
     B.print("B:");
     }
   };

Another (more brittle) solution is to use a common matrix, then assign the memory to other matrices using C++11 std::move(). For example:

#include <utility>
#include <armadillo>

using namespace std;
using namespace arma;

int main()
  {
  mat C(4,5, fill::zeros);  // C is the common matrix

  mat A:
  mat B;      

  A = std::move( mat(C.memptr(), C.n_rows, C.n_cols, false, false) );
  B = std::move( mat(C.memptr(), C.n_rows, C.n_cols, false, false) );

  // note: in the above, the last argument of 'false' is important

  A(1,1) = 1;
  B(2,2) = 2;

  // A and B will both have 1 and 2 as they're using the same memory      

  A.print("A:");
  B.print("B:");
  }

If you're using gcc or clang, you can enable C++11 mode with the -std=c++11 switch.

回答2:

In vs 2013,

#define ARMA_USE_CXX11

should be included. And then std::move would work.

Thanks hbrerkere for guiding right way.

来源：https://stackoverflow.com/questions/34896324/how-to-share-common-memory-in-armadillo

标签

c++

armadillo