[Bug c++/71010] error: 'begin' was not declared in this scope

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71010

Jonathan Wakely <redi at gcc dot gnu.org> changed:

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

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
No, it's not a bug. Range-based 'for' is not supposed to find std::begin and
std::end unless std is an associated namespace.

Furthermore, your code has undefined behaviour, it is forbidden to add your own
functions to namespace std. The correct way to do it is to write the begin/end
overloads in the same namespace as your type (in this case that's the global
namespace).

class X
{
  int m_x[5] = { 0, 1, 2, 3, 4 };
public:
  int* first() { return &m_x[0]; }
  int* last() { return &m_x[4]; }
};

int* begin(X& x) { return x.first(); }
int* end(X& x) { return x.last(); }

This works with all versions of GCC that support C++11.