On 01/11/2012 07:44 PM, Christopher Jefferson wrote:
On 11 Jan 2012, at 18:28, lcaminiti wrote:
Hello all,
Many of Boost macro APIs PP_CAT symbols with either __LINE__ or __COUNTER__ to make them unique (MPL_STATIC_ASSERT, SCOPE_EXIT, etc). AFAIK, __LINE__ is C++03 standard while __COUNTER__ is only a MSVC extension. I think using __COUNTER__ instead of __LINE__ might allow to expand a macro multiple times on the same line... but a part from that:
What's the reason for using __COUNTER__ on MSVC instead of just using __LINE__ for all compilers?
__LINE__ is restarted for each header file separately, so you can get problems with using a macro on the same line number of different files. I've been bitten by this before. __COUNTER__ is superior.
__COUNTER__ is only per TU, and careless usage can easily lead to ODR violations.