How to get a pointer for 2D array of QVector?

[amleto]

I was a little confused, and now understand what your codes mean.

A basic question: If an array is created with FortranMatrix as follows

void cppFN()
{
    FortranMatrix < int, 3, 5 >  intArray;
 
    intArray(1,2) =1;
    ...
}

void cppFN()
{
    FortranMatrix < int, 3, 5 >  intArray;

    intArray(1,2) =1;
    ...
}

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a user does not need to delete the intArray. It will be cleared by OS when leaving the cppFN(). Is my understanding correct?

Yes, correct.

but remember that in cpp code, you should be using 'at' to access the array elements, e.g

void cppFN()
{
    FortranMatrix < int, 3, 5 >  intArray;
 
    intArray.at(1,2) = 1; // not 'intArray(1,2)' <-- fortran-only syntax
    ...
}

void cppFN()
{
    FortranMatrix < int, 3, 5 >  intArray;

    intArray.at(1,2) = 1; // not 'intArray(1,2)' <-- fortran-only syntax
    ...
}

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[d_stranz]

but remember that in cpp code, you should be using 'at' to access the array elements, e.g

No, I think you woke up too early (or maybe are staying awake much too late).

The code refers to your FortranMatrix template class, which has template methods for operator()( int, int ). His code is exactly correct for that class - the internal storage for that class is a C++ array allocated by operator new(), and the template class doe not define an "at()" method.

[amleto]

No, I think you woke up too early (or maybe are staying awake much too late).

The code refers to your FortranMatrix template class, which has template methods for operator()( int, int ). His code is exactly correct for that class - the internal storage for that class is a C++ array allocated by operator new(), and the template class doe not define an "at()" method.

I think you are confused.

I know it refers to my FortranMatrix, which has operator()(...) ONLY for fortran - it is commented as such. Lets remind ourselves:

I'd be interested in how well this works:

template<class T, unsigned int M, unsigned int N>
class FortranMatrix
{
public:
  FortranMatrix()
    :array_(new T[M][N])
  {}
 
  // cpp interface
  T& at(unsigned int x, unsigned int y)
  {
    return (array_)[x][y];
  }
 
  // fortran interface - transpose it
  T& operator()(unsigned int x, unsigned int y)
  {
    return (array_)[y][x];
  }
 
  //pass the matrix to a fortran method accepting a T*
  operator T*()
  {
    return &(*array_)[0];
  }
 
private:
  T (*array_)[N];
};

template<class T, unsigned int M, unsigned int N>
class FortranMatrix
{
public:
  FortranMatrix()
    :array_(new T[M][N])
  {}

  // cpp interface
  T& at(unsigned int x, unsigned int y)
  {
    return (array_)[x][y];
  }

  // fortran interface - transpose it
  T& operator()(unsigned int x, unsigned int y)
  {
    return (array_)[y][x];
  }

  //pass the matrix to a fortran method accepting a T*
  operator T*()
  {
    return &(*array_)[0];
  }

private:
  T (*array_)[N];
};

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Quite clearly there IS a method 'at'. Funnily enough, I commented that this method to be used in cpp code, which is why I remarked that this method, and not operator()(...), should be used.

Regards

[d_stranz]

Quite clearly there IS a method 'at'.

And equally clear is the fact that I was the one up too early to be typing comments into the forum...

[tfmp]

Thank you for all replies and comments, given above. The issue regrading data-sharing between Fortran and C++ is resolved.