[Bug c++/51352] New: g++ can't pass variable-length array as a function argument

[Bug c++/51352] New: g++ can't pass variable-length array as a function argument

[jvgreen at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51352

             Bug #: 51352
           Summary: g++ can't pass variable-length array as a function
                    argument
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jvgreen@gmail.com


According to http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html, gcc
supports variable-length arrays as an extension when compiling C++ code.  An
example is given on that page of how to pass such an array as an argument to a
function.  However, I haven't been able to get it to work.  As an example, the
simple program

  #include <iostream>
  #include <cstdlib>

  void fill_array(int dim, int array[dim][dim]);

  int main(int argc, char *const argv[]) {
    int dim = atoi(argv[1]);
    int array[dim][dim];
    fill_array(dim, array);
    for(int i = 0; i < dim; ++i) {
      for(int j = 0; j < dim; ++j) {
        std::cout << array[i][j] << "\n";
      }
    }
  }

  void fill_array(int dim, int array[dim][dim]) {
    int counter = 0;
    for(int i = 0; i < dim; ++i) {
      for(int j = 0; j < dim; ++j) {
        array[i][j] = counter++;
      }
    }
  }

won't compile under g++ version 4.6.1 (I think that's the version I was
running), despite what that page claims, instead giving errors claiming that
the parameter dim is being used outside the function.  (gcc in C99 mode can
compile the code.)

[Bug c++/51352] g++ can't pass variable-length array as a function argument

[jvgreen at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51352

--- Comment #1 from Joshua Green <jvgreen at gmail dot com> 2011-11-30 06:23:40 UTC ---
(Of course, compiling under gcc requires replacing
  #include <iostream>
  #include <cstdlib>
with
  #include <stdio.h>
  #include <stdlib.h>
and
  std::cout << array[i][j] << "\n";
with
  printf("%d\n", array[i][j]);
but I suppose that that was implied.)

[Bug c++/51352] g++ can't pass variable-length array as a function argument

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51352

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-11-30 09:32:23 UTC ---
This might just be a documentation bug if G++ supports declaring VLAs at block
scope but not as function arguments. No version from 4.1 onwards has supported
it

[Bug c++/51352] g++ can't pass variable-length array as a function argument

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51352

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-12-14
     Ever Confirmed|0                           |1

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-12-14 23:49:49 UTC ---
Confirmed.

[Bug c++/51352] g++ can't pass variable-length array as a function argument

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51352

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ian at rhymneyconsulting dot co.uk

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> ---
*** Bug 61788 has been marked as a duplicate of this bug. ***

[Bug c++/51352] g++ can't pass variable-length array as a function argument

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51352

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
We have this comment in cp_parser_direct_declarator:

          /* Normally, the array bound must be an integral constant
             expression.  However, as an extension, we allow VLAs
             in function scopes as long as they aren't part of a
             parameter declaration.  */
          cp_parser_error (parser,
                   "array bound is not an integer constant");

thus the limitation is well known (to the author of the parser at least ;)

[Bug c++/51352] g++ can't pass variable-length array as a function argument

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51352

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |cdkrot at yandex dot ru

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 62295 has been marked as a duplicate of this bug. ***