[Bug c++/17453] New: G++ type conversion bug

[Bug c++/17453] New: G++ type conversion bug

[froloff at os2 dot ru]

The folowing source produce an error in line 10 during compilation
=====================================================================
test.c: In function `void chk_gcc_bug()':
	test.c:7: error: cannot convert `std::vector<_Tp, _Alloc>::begin() [with _Tp =
	unsigned char, _Alloc = std::allocator<unsigned char>]()' from type `
	__gnu_cxx::__normal_iterator<unsigned char*, std::vector<unsigned char,
	std::allocator<unsigned char> > >' to type `unsigned char*'
====>8====================================>8=========================
#include <vector>

typedef std::vector<unsigned char> byte_vector;

void chk_gcc_bug()
{
  byte_vector v(96 / 8);
  unsigned char *ptr;

  ptr= (unsigned char *)v.begin();
  ptr= &(*(v.begin()));
}
====>8====================================>8=========================
Also check with gcc3.3.3 with the same result
Compiled fine with MSC v7.0

-- 
           Summary: G++ type conversion bug
           Product: gcc
           Version: 3.2.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: froloff at os2 dot ru
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17453

[Bug c++/17453] G++ type conversion bug

[caj at cs dot york dot ac dot uk]

------- Additional Comments From caj at cs dot york dot ac dot uk  2004-09-13 11:34 -------
There is no reason why you should be able to cast an iterator to a pointer. msc
v7.0 must use a "pure pointer" as iterators while g++ doesn't. This isn't a bug.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17453

[Bug c++/17453] G++ type conversion bug

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-09-13 11:35 -------
Yes, and g++ has also a very good reason for not doing it: in debug mode, we 
detect uses of invalid iterators and stuff, and raw pointers could not do that.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17453

[Bug c++/17453] G++ type conversion bug

[froloff at os2 dot ru]

------- Additional Comments From froloff at os2 dot ru  2004-09-13 12:15 -------
(In reply to comment #1)
> There is no reason why you should be able to cast an iterator to a pointer. msc
> v7.0 must use a "pure pointer" as iterators while g++ doesn't. This isn't a bug.

I didn't wait that it convert iterator to pointer by simple assignment, co I add
cast manually, and didn't saw any reaon why G++ can cast it.
So How I can read a number of vector elements? Or You propose to read it into
temp array of chars and the make assignment manually?


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17453

[Bug libstdc++/17453] G++ type conversion bug

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-09-13 13:24 -------
Gcc doesn't do the conversion because the standard doesn't specifically 
say it has to be able to. Our implementation uses some optimizations 
that don't allow this simple conversion, because our iterations aren't 
just pointers. 
 
The solution to your problem is to either do an element-wise copy, or 
if you are adventurous, use 
  &*vec.begin(); 
to get the address of the first element. 
 
W. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
          Component|c++                         |libstdc++
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17453

[Bug libstdc++/17453] G++ type conversion bug

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-09-13 13:47 -------
> So How I can read a number of vector elements? Or You propose to read it into
> temp array of chars and the make assignment manually?

&v[0] is always an unsigned char* pointing to contiguous memory. But this is 
not a question for GCC Bugzilla. I suggest you to buy some good STL book, or 
ask similar questions in comp.lang.c++.moderated.



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17453

[Bug libstdc++/17453] G++ type conversion bug

[froloff at os2 dot ru]

------- Additional Comments From froloff at os2 dot ru  2004-09-14 06:42 -------
Thanks to all for Your replays.
Best regards
Dmitry

PS
> &v[0] is always an unsigned char* pointing to contiguous memory. 
I know about that, as You can see from attached source (line 11) ;)




-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17453