Working with Mark’s dnl code, we came across an interesting issue. Mark had used the stl::set class for some of his code and whilst it compiled fine under Visual Studio, it failed to compile under gcc/g++. With the error:
dnlCommon/Logger.cpp: In member function 'void dnlCommon::Logger::setMask(std::ostream&, std::bitset<5ul>)': dnlCommon/Logger.cpp:64: error: invalid initialization of reference of type 'dnlCommon::Logger::LoggerPair&' from expression of type 'const dnlCommon::Logger::LoggerPair' /usr/local/lib/gcc-4.0.4/include/c++/bits/stl_algo.h: In function '_OutputIterator std::remove_copy(_InputIterator, _InputIterator, _OutputIterator, const _Tp&) [with _InputIterator = std::_Rb_tree_const_iterator<dnlCommon::Logger::LoggerPair>, _OutputIterator = std::_Rb_tree_const_iterator<dnlCommon::Logger::LoggerPair>, _Tp = dnlCommon::Logger::LoggerPair]': /usr/local/lib/gcc-4.0.4/include/c++/bits/stl_algo.h:1112: instantiated from '_ForwardIterator std::remove(_ForwardIterator, _ForwardIterator, const _Tp&) [with _ForwardIterator = std::_Rb_tree_const_iterator<dnlCommon::Logger::LoggerPair>, _Tp = dnlCommon::Logger::LoggerPair]' dnlCommon/Logger.cpp:54: instantiated from here /usr/local/lib/gcc-4.0.4/include/c++/bits/stl_algo.h:1037: error: passing 'const dnlCommon::Logger::LoggerPair' as 'this' argument of 'dnlCommon::Logger::LoggerPair& dnlCommon::Logger::LoggerPair::operator=(const dnlCommon::Logger::LoggerPair&)' discards qualifiers
It turned out that the issue occurred with the assignment operator (operator = ) on the
stl::set class. Tracing the problem we found that
const rather than non cost. Hence calling stl functions that made use of the iterators but also the assignment operator would fail.
Looking further into the problem I found:
// _GLIBCXX_RESOLVE_LIB_DEFECTS // DR 103. set::iterator is required to be modifiable, // but this allows modification of keys. typedef typename _Rep_type::const_iterator iterator; typedef typename _Rep_type::const_iterator const_iterator;
Hmm, that’s strange. A bit of googling revieled the problem to be an issue with the stl standard. Fixes to gcc/g++ are listed at http://gcc.gnu.org/onlinedocs/libstdc++/ext/howto.html in particular error 103 is listed at http://gcc.gnu.org/onlinedocs/libstdc++/ext/lwg-defects.html#103
So it looks like the bug was ratified by the C++ committee in 1998 and it still isn’t fixed in Visual Studio 2005 (VC++ 8.0) !
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