Auto-discovery of include files is not working

]I'm having an include path problem trying to build Qt C++ projects in both Qt Creator and Eclipse. (I'm using Linux, the gcc toolchain and Qt4.6.2.) An interesting feature of the problem is that I have been able to create a new project, add code and libraries and build and run it once. If I then make a change to my code and try to recompile, I get about 100 compiler errors like the following:

/usr/include/c++/4.5/cstring:76:11: error: ‘::memchr’ has not been declared
/usr/include/c++/4.5/cstring:77:11: error: ‘::memcmp’ has not been declared
/usr/include/c++/4.5/cstring:78:11: error: ‘::memcpy’ has not been declared
/usr/include/c++/4.5/cstring:79:11: error: ‘::memmove’ has not been declared
/usr/include/c++/4.5/cstring:80:11: error: ‘::memset’ has not been declared
/usr/include/c++/4.5/cstring:81:11: error: ‘::strcat’ has not been declared
...

When I build my own C++ projects in Eclipse I see path discovery activity like this:

GNU C++ (SUSE Linux) version 4.5.0 20100521 [gcc-4_5-branch revision 159657] (x86_64-suse-linux)
compiled by GNU C version 4.5.0 20100521 [gcc-4_5-branch revision 159657], GMP version 4.3.2, MPFR version 2.4.2, MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/4.5
/usr/include/c++/4.5/x86_64-suse-linux
/usr/include/c++/4.5/backward
/usr/local/include
/usr/lib64/gcc/x86_64-suse-linux/4.5/include
/usr/lib64/gcc/x86_64-suse-linux/4.5/include-fixed
/usr/lib64/gcc/x86_64-suse-linux/4.5/../../../../x86_64-suse-linux/include
/usr/include
End of search list.
...

This activity does not seem to take place when compiling Qt-based projects. In fact, the only way I've been able to build consistently is to use Eclipse to convert my Qt Gui project into a c++ project (File|New|Convert to a C++ Project). That, in itself, was a valuable exercise as I learned something about the Qt dependencies, but, perhaps a bit too much work. I obviously missed some important documentation. Can anyone point me in the right direction?

Thanks.

Guessing here, but gcc 4.5 is the very latest version of the Gnu compiler collection. It's quite possible that something has changed, say in the compiler flags, that qmake hasn't caught up with yet. It's vaguely possible that there's something wrong with your gcc installation, but I'd start with your specific qmakespec conf file and see if the settings used are consistent with those used by eclipse.

Thanks. I recently upgraded from gcc 4.3. The problem existed in both versions of the toolchain.