In message <033901c50655$6347e4d0$0300000a@pc>, Terje Slettebø <tslettebo@broadpark.no> writes
From: "Preston A. Elder" <prez@neuromancy.net> [...] struct my_type { int a; int b; };
template<typename C, typename T> std::basic_istream<C,T> &operator>>(std::basic_istream<C,T> &is, my_type &mt) { is >> mt.a >> mt.b; return is; } [...] The output I get is: TEST 1 FAILED TEST 2: 3 4 [...] My investigation has shown that this occurs because boost::lexical_cast calls stream.unsetf(std::ios::skipws);
Yes, lexical_cast unsets the skipping of whitespace, but that does not, to my knowledge, introduce problems for correctly written stream extraction operators. If reading a representation in and writing it out for a custom type depends on the skipping of whitespace, the stream extraction operator must guarantee this -- it cannot assume the state of the input stream will be what it needs. In other words, there is a bug in the implementation of operator>>. Here is a simplified (untested and not exception safe) sketch of the basic logic: ... operator>>(... &is, my_type &mt) { std::ios::fmtflags old_fmt = is.flags(); is.setf(std::ios::skipws); is >> mt.a >> mt.b; is.flags(old_fmt); return is; } HTH Kevlin -- ____________________________________________________________ Kevlin Henney phone: +44 117 942 2990 mailto:kevlin@curbralan.com mobile: +44 7801 073 508 http://www.curbralan.com fax: +44 870 052 2289 Curbralan: Consultancy + Training + Development + Review ____________________________________________________________