Re: copy_n should result in a one past the end input iterator

[Jonathan Wakely]

On 21/11/16 03:10 +, Robert Young wrote:

/*
gcc -Wall -Wextra -std=c++11 copy_n_vs_copy.cpp -lstdc++ -o copy_n_vs_copy

One Past the End
https://gcc.gnu.org/onlinedocs/libstdc++/manual/iterators.html#iterators.predefined.end

BUG location:
/usr/lib/gcc/x86_64-pc-linux-gnu/5.1.0/include/g++-v5/bits/stl_algo.h

*/


Hi,

This mailing list is for automated email from our Bugzilla database,
if you send email to this list it is likely to be missed or ignored.

Please report bugs to Bugzilla as described at
https://gcc.gnu.org/bugs/

However, this is not a bug because it is unclear what the right
behaviour is for this algorithm, see
http://cplusplus.github.io/LWG/lwg-active.html#2471

We are not going to change libstdc++ until the C++ standards committee
decides what the right behaviour is.

copy_n should result in a one past the end input iterator

[Robert Young]

/*
gcc -Wall -Wextra -std=c++11 copy_n_vs_copy.cpp -lstdc++ -o copy_n_vs_copy

One Past the End
https://gcc.gnu.org/onlinedocs/libstdc++/manual/iterators.html#iterators.predefined.end

BUG location:
/usr/lib/gcc/x86_64-pc-linux-gnu/5.1.0/include/g++-v5/bits/stl_algo.h

*/

#include 
#include 
#include 
#include 

int main()
 {
  std::string i("abc");
  std::string o;
  std::istringstream t;

  t=std::istringstream(i);
  o.clear();
  assert(3==t.rdbuf()->in_avail());
  std::copy(std::istreambuf_iterator(t.rdbuf()),
   std::istreambuf_iterator(),back_inserter(o));
  std::cout<<"Test1(copy):\tResult_size:"in_avail());
  std::copy_n(std::istreambuf_iterator(t.rdbuf()),
   3,back_inserter(o));
  std::cout<<"Test2(copy_n):\tResult_size:" 0)
-   ++__first;
- else
+ ++__first;
+ if (--__n <= 0)
break;
}
}