C

C++

unsigned long* ulp = (unsigned long*)&n;
bitset<32> bits_less_signif (*ulp);
ulp++;
bitset<32> bits_most_signif (*ulp);
cout << bits_most_signif << bits_less_signif << endl;

gcc

• src (Icelandic GNU mirror)
• installation doc
• manual
• C++ library doc at gnu.org
• perl script determining which ld is used by gcc (Solaris/SunOS)
• to see (very verbose) linker output, use -Wl,-verbose option for gcc
• to get a list of gcc predefined symbols (used for platform identification etc.): gcc -E -dM - < /dev/null
• to remove dynamic dependency on libgcc_s.so, compile with -static-gcc flag
• -O3 seems to improve drastically (compared to -O2) the speed of C++ code (and seems does not have much effect on C code)

gcc problems

• if linking shared library and getting ld: fatal: relocations remain against allocatable but non-writable sections this means that one tries to link into shared library non-pic objects; those objects should be (re)compiled with -fpic or -fPIC options (observed on Solaris)
• if getting weird craches upon exit from C library, recompile gcc with --enable-__cxa_atexit option (relevant on Linux only).
• if getting weird unresolved symbols like _ZNSs4_Rep20_S_empty_rep_storageE at runtime, try to (re)compile against static libstdc++.
• a run-time error undefined symbol: __dso_handle caused by incompatibility between gcc and binutils, and triggered in presence of some specific gcc flags (notably -nostdlib). Upgrade to the latest binutils (from the gcj FAQ).
• if having inconsistent floating point results, or other floating point issues, the option -ffloat-store may help; for details, see links at the relevant portion of gcc docs.
• error expected ')' before string constant (usually in old code) probably caused by code like printf (__FUNCTION__" bla-bla"); in old gcc's (prior 3.4?), __FUNCTION__ was a string literal, and in recent gcc's it is a variable; so this code should be replaced by printf ("%s bla-bla", __FUNCTION__)