Re: Iterators wrappers?

[Paolo Carlini <pcarlini at suse dot de>]

Hi,

> I am currently working on some test cases for some functions in the 
> algorithm header. I wondered if there exists any "exact iterator 
> checkers", which (for example) given the begin() and end() iterators 
> for a vector would only reveal exactly the required features of a 
> bidirectional iterator and perhaps also further check for things like 
> an iterator being moved after end() or before begin(). Such things 
> would allow for more easily testing if an algorithm is using exactly 
> the properties it is allowed to.

In 3.4.x, to help the programmer with this kind of issues, besides the 
compile-time concept-checks, we have a new, powerful, run-time debug mode:

   http://gcc.gnu.org/onlinedocs/libstdc++/debug.html

To give you a stupid, trivial example, this snippet compiled with 
-D_GLIBCXX_DEBUG:

#include <vector>
int main()
{
 std::vector<int> v;
 std::vector<int>::iterator it = v.end();
 *it;
}

leads, at run time, to:

/usr/local/gcc-341/lib/gcc/i686-pc-linux-gnu/3.4.1/../../../../include/c++/3.4.1/debug/safe_iterator.h:178:
   error: attempt to dereference a past-the-end iterator.

Objects involved in the operation:
iterator "this" @ 0x0xbffff690 {
type = 
N11__gnu_debug14_Safe_iteratorIN9__gnu_cxx17__normal_iteratorIPiN10__gnu_norm6vectorIiSaIiEEEEEN15__gnu_debug_def6vectorIiS6_EEEE 
(mutable iterator);
 state = past-the-end;
 references sequence with type `N15__gnu_debug_def6vectorIiSaIiEEE' @ 
0x0xbffff690
}
Abort

/////////////////

Paolo.