Consider the code: #include <map>
class a { public: a(); }; class b { public: // implicit default ctor bool operator<(const b& rhs) const; private: a a_val; }; typedef std::map<b, int> my_map; void func() { my_map::value_type x; } That compiled correctly with 4.3.2. It fails to compile with pre-4.4 trunk: Using built-in specs. Target: i686-linux Configured with: ../trunk/configure --enable-languages=c,c++ --build=i686-linux --host=i686-linux --target=i686-linux --prefix=/g/users/cgd/proj/gcc-trunk/bld/../inst Thread model: posix gcc version 4.4.0 20081123 (experimental) (GCC) with the error: In file included from [...]/bin/../lib/gcc/i686-linux/4.4.0/../../../../include/c++/4.4.0/bits/stl_algobase.h:71, from [...]/bin/../lib/gcc/i686-linux/4.4.0/../../../../include/c++/4.4.0/bits/stl_tree.h:67, from [...]/bin/../lib/gcc/i686-linux/4.4.0/../../../../include/c++/4.4.0/map:65, from test2.cc:1: [...]/bin/../lib/gcc/i686-linux/4.4.0/../../../../include/c++/4.4.0/bits/stl_pair.h: In constructor 'std::pair<_T1, _T2>::pair() [with _T1 = const b, _T2 = int]': test2.cc:20: instantiated from here [...]/bin/../lib/gcc/i686-linux/4.4.0/../../../../include/c++/4.4.0/bits/stl_pair.h:84: error: uninitialized member 'std::pair<const b, int>::first' with 'const' type 'const b' Looking at the preprocessed source (which i'll attach shortly), I see that pair's default ctor is: pair() : first(), second() { } I don't know if that's "right," but the C++98 std says that: "Initializes its members as if implemented: pair() : first(T1()), second(T2()) {}" (20.2.2, paragraph 2.) If I change the pair() ctor to be: pair() : first(_T1()), second(_T2()) { } (by hacking the preprocessed source), the result compiles correctly. (I'm *so* far from an expert on STL that I'm not 100% sure that sample code is actually valid, but on its face it seems reasonable at least, and 4.3.x accepted it, and Comeau's test drive accepts it as well.) -- Summary: 'map' value type + new uninitted const member warnings causes error Product: gcc Version: 4.4.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: cgd at google dot com GCC build triplet: i686-linux GCC host triplet: i686-linux GCC target triplet: i686-linux http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38233