Re: [ROOT] passing table

From: Christian Holm Christensen (cholm@hehi03.nbi.dk)
Date: Sun Sep 07 2003 - 13:20:59 MEST 

Hi Christian,

cstrato <aon.912121399@aon.at> wrote concerning
  [ROOT] passing table [Sat, 06 Sep 2003 21:08:22 +0200] 
----------------------------------------------------------------------
> Sorry for this non root question:
> I have a function:
>    void MyFunction(Int_t n, Int_t m, Double_t **table)
> 
> Usually I create the table on the heap an pass it to MyFunction().
> However, when I create the table on the stack:
>    Double_t table[4][8]
> I am unable to pass it to MyFunction()

The conversion from `double(*)[]' to `double**' isn't legal.  In the
first case, you have a specific memory layout, while in the latter, it
is completely arbitrary.  

> you know how to pass the table to MyFunction()?

I would suggest using `calculated index', or perhaps `std::valarray'.
For the former, see the attached file. 

Yours, 

 ___  |  Christian Holm Christensen 
  |_| |	 -------------------------------------------------------------
    | |	 Address: Sankt Hansgade 23, 1. th.  Phone:  (+45) 35 35 96 91
     _|	          DK-2200 Copenhagen N       Cell:   (+45) 24 61 85 91
    _|	          Denmark                    Office: (+45) 353  25 305
 ____|	 Email:   cholm@nbi.dk               Web:    www.nbi.dk/~cholm
 | |



#include <iostream>
#include <iomanip>
#include <vector>

void function(double** array, size_t n, size_t m) 
{
  std::cout << "Array of size (" << n << "x" << m << "): " << std::endl;
  for (size_t i = 0; i < n; ++i) {
    for (size_t j = 0; j < m; ++j) 
      std::cout << std::setw(3) << array[i][j] << std::flush;
    std::cout << std::endl;
  }
} 

void function(double* array, size_t n, size_t m) 
{
  std::cout << "Array of size (" << n << "x" << m << "): " << std::endl;
  for (size_t i = 0; i < n; ++i) {
    for (size_t j = 0; j < m; ++j) 
      std::cout << std::setw(3) << array[i * n + j] << std::flush;
    std::cout << std::endl;
  }
}

int main() 
{
  double** a1 = new double*[3];
  for (size_t i = 0; i < 3; ++i)  {
    a1[i] = new double[2];
    for (size_t j = 0; j < 2; ++j) 
       a1[i][j] = i * 10 + j;
  }

  function(a1, 3, 2);

  double a2[2][3];
  for (size_t i = 0; i < 2; ++i) 
    for (size_t j = 0; j < 3; ++j) 
      a2[i][j] = 10 * j + i;

  // function(&(a2[0]), 2, 3);

  double a3[6];
  for (size_t i = 0; i < 2; ++i) 
    for (size_t j = 0; j < 3; ++j) 
      a3[i * 2 + j] = 10 * j + i;

  function(a3, 2, 3);

  return 0;
}

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