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? Thanks a lot. --Lorenzo -- View this message in context: http://boost.2283326.n4.nabble.com/boost-COUNTER-vs-LINE-tp4286398p4286398.h... Sent from the Boost - Dev mailing list archive at Nabble.com.
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. Chris
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.
On Wednesday, January 11, 2012 10:28:25 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?
MSVC has problems with expanding __LINE__ when precompiled headers are used. Basically, __COUNTER__ is the only practical option with this compiler when the macro is to be expanded in a header.
On 11.01.2012 20:06, Andrey Semashev wrote:
On Wednesday, January 11, 2012 10:28:25 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?
MSVC has problems with expanding __LINE__ when precompiled headers are used. Basically, __COUNTER__ is the only practical option with this compiler when the macro is to be expanded in a header.
As I recall, the problem is when the option for edit-and-continue is used. I had that problem with Petru Marginean's original ScopeGuard code. With the edit-and-continue option, Visual C++ really messed up the explansion of __LINE__, so that the ScopeGuard temporary names became invalid. Cheers, - Alf
Andrey Semashev-2 wrote
On Wednesday, January 11, 2012 10:28:25 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?
MSVC has problems with expanding __LINE__ when precompiled headers are used. Basically, __COUNTER__ is the only practical option with this compiler when the macro is to be expanded in a header.
OK. Is there a Boost macro like this already? #include <boost/config.hpp> #ifdef BOOST_MSVC # define BOOST_LINE_COUNTER __COUNTER__ #else # define BOOST_LINE_COUNTER __LINE__ #endif Thanks. --Lorenzo -- View this message in context: http://boost.2283326.n4.nabble.com/boost-COUNTER-vs-LINE-tp4286398p4293111.h... Sent from the Boost - Dev mailing list archive at Nabble.com.
On Jan 13, 2012, at 2:16 PM, lcaminiti wrote:
OK. Is there a Boost macro like this already?
#include <boost/config.hpp>
#ifdef BOOST_MSVC # define BOOST_LINE_COUNTER __COUNTER__ #else # define BOOST_LINE_COUNTER __LINE__ #endif
__COUNTER__ is also available in gcc4.3 and later. http://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html#Common-Prede... I don't know how precisely it matches the MSVC __COUNTER__ in various cases like pre-compiled headers and the like.
participants (6)
-
Alf P. Steinbach -
Andrey Semashev -
Christopher Jefferson -
Kim Barrett -
lcaminiti -
Mathias Gaunard