A proper way to create a matrix in c++

Question

I want to create an adjacency matrix for a graph. Since I read it is not safe to use arrays of the form matrix[x][y] because they don\'t check for range, I deci

Answer 1

If you want 'C' array performance, but with added safety and STL-like semantics (iterators, begin() & end() etc), use boost::array.

Basically it's a templated wrapper for 'C'-arrays with some NDEBUG-disable-able range checking asserts (and also some std::range_error exception-throwing accessors).

I use stuff like

boost::array,4> m;

instead of

float m[4][4];

all the time and it works great (with appropriate typedefs to keep the verbosity down, anyway).

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UPDATE: Following some discussion in the comments here of the relative performance of boost::array vs boost::multi_array, I'd point out that this code, compiled with g++ -O3 -DNDEBUG on Debian/Lenny amd64 on a Q9450 with 1333MHz DDR3 RAM takes 3.3s for boost::multi_array vs 0.6s for boost::array.

#include 
#include 
#include "boost/array.hpp"
#include "boost/multi_array.hpp"

using namespace boost;

enum {N=1024};

typedef multi_array M;
typedef array,N>,N> C;

// Forward declare to avoid being optimised away
static void clear(M& m);
static void clear(C& c);

int main(int,char**)
{
  const clock_t t0=clock();

  {
    M m(extents[N][N][N]);
    clear(m);
  }

  const clock_t t1=clock();

  {
    std::auto_ptr c(new C);
    clear(*c);
  }

  const clock_t t2=clock();

  std::cout 
    << "multi_array: " << (t1-t0)/static_cast(CLOCKS_PER_SEC) << "s\n"
    << "array      : " << (t2-t1)/static_cast(CLOCKS_PER_SEC) << "s\n";

  return 0;
}

void clear(M& m)
{
  for (M::index i=0;i