Re: 2d VLA argument, void f( int m, int n, int a[m][n] ) ?

[FÖLDY Lajos]

On Mon, 10 Aug 2009, denis wrote:

> Folks,
>  how can I pass a 2d array with sizes, like
>
> void f( int m, int n, int a[m][n] )
> {
>    ... a[j][k] = ...
> ?
> I see claims that this is valid C99, but g++-4.2.1 gives
>    error: ?m? was not declared in this scope
>
> So, how can I make this work ?
> I don't care much about the function header or call syntax,
> but a[j][k] in the body should work as fast as a[j*n+k] .
> (Some suggest boost::multi_array -- anyone have an example of such an f
> () with that ?)
>
> cheers
>  -- denis

/tmp> cat 1.c
#include <stdio.h>

void f( int m, int n, int a[m][n] )
{
  a[2][3]=12345;
}

int main()
{
  int a[5][6];
  f(5,6,a);
  printf("%d\n", a[2][3]);
}

/tmp> gcc-4.2.3 1.c && ./a.out
12345


So, what is the problem? :-)

regards,
lajos