Re: [boost] Bug with gcc and array

Subject: Re: [boost] Bug with gcc and array
From: Niels Dekker - mail address until 2010-10-10 (niels_address_until_2010-10-10_at_[hidden])
Date: 2008-11-24 08:39:47

Andreas Klein wrote:
> I have found a strange limitation for the size of an array. The error
> is the same both for boost 1.36 and for the array in gcc 4.3.2 (and in
> the gcc 4.4 snapshot I use). I am almost sure that it is a bug of gcc
> and not of the array implementation.
>
> Here is the code.
>
> #include<array>
> using namespace std;
>
>
> int main () {
>   array<unsigned int, (1<<22)> a; // Create a big array
>
>   a[(1<<22)-13]=0;  // This give a segmantation fault
> }
>
> In contrast a C-array works fine.
>
> int main () {
>   unsigned int  a[1<<22];
>
>   a[(1<<22)-13]=0;
> }
>
> Since the naturale implementation of the array class is just a wrapper
> around the C-style array this is very strange.
>
> I tryed to track down the bug. You use the following implementation:
>
>   template<typename T, unsigned int n> class array {
>     T C[n];
>
>   public:
>     typedef unsigned int size_type;
>     T& operator[](size_type p) {
>       return C[p];
>     }
>   };

I have no clue.  But what does GCC do when you try the following?

  struct big_array {
    unsigned int C[1<<22];
    unsigned int& operator[](unsigned p) {
       return C[p];
    }
  };

  int main () {
   big_array a;
   a[(1<<22)-13]=0;  // ???
 }

Kind regards,
--
Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center