Re: Q: Prototype & function calls for multi-dimensional arrays. Best way?

From:
"Alf P. Steinbach" <alfps@start.no>
Newsgroups:
comp.lang.c++
Date:
Fri, 09 Nov 2007 09:01:28 +0100
Message-ID:
<13j84r4713qm527@corp.supernews.com>
* James Tursa:

MVC 8.0
Windows XP

I would like to use multidimensional arrays in a function call. This
method works:

//-------------------------------------------------------------------------
void fun(double *d, int m, int n);

extern int main(void)


Don't do 'extern' there.

Also, although formally allowed, 'void' as indication of no arguments is
C'ism, best a'voided. In C++ no arguments is indicated by no arguments.

{
    double a[2][3] = {1.0,2.0,3.0,4.0,5.0,6.0};
    double b[3][4] =
{1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0,11.0,12.0};

    fun( (double *) a, 2 ,3);
    fun( (double *) b ,3, 4);
}

void fun(double *d, int m, int n)
{
    // code here to work with d as an m x n matrix.
    return;
}
//----------------------------------------------------------------------

But what I would really like to do is avoid the cast in the fun call
(mainly for readability and ease of programming). I.e., I would like
to change these lines:

    fun((double *)a,2,3);
    fun((double *)b,3,4);

into these lines:

    fun(a,2,3);
    fun(b,3,4);

and have the function interface be able to handle it. Is there a way
to set up the function interface to do this?


A great many ways.

For the particular example above the simplest would probably be a
templated function taking the matrix by reference,

   template< size_t N, size_t M >
   void fun( double (&d)[N][M] ) { ... }

But if you're going to matrices and are confounded by this problem, I
suggest you use some ready-made matrix library.

Cheers, & hth.,

- Alf

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