http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58236
Bug ID: 58236 Summary: -Wuninitialized doesn't report uninitialised variable as expected Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: noufal at nibrahim dot net.in Created attachment 30695 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30695&action=edit Test case program Command run ----------- gcc was run like so gcc -Wall program.c I also tried running gcc -Wuninitialized program.c The program is attached to this bug report. Behaviour --------- #include <stdio.h> void test() { int iters; while(iters++ <= 100) { printf("%d\n", iters); } } int main() { test(); return 0; } In the program above, the 'iters' variable is not initialised. This makes the loop sometimes behave in unexpected ways. Ideally, the -Wuninitialized option should warn about this. This doesn't happen. With clang, I get the following output noufal@sanitarium% clang -Wall program.c program.c:7:9: warning: variable 'iters' is uninitialized when used here [-Wuninitialized] while(iters++ <= 100) { ^~~~~ program.c:5:12: note: initialize the variable 'iters' to silence this warning int iters; ^ = 0 1 warning generated. I tested this with the stock Debian gcc (4.6.3) but friends have tried it on 4.6, 4.7 and 4.8 and reported the same problem. gcc -v output -------------- Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Debian 4.6.3-1' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++,go --prefix=/usr --program-suffix=-4.6 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-plugin --enable-objc-gc --with-arch-32=i586 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.6.3 (Debian 4.6.3-1) System type ----------- uname -a output: Linux sanitarium 3.1.0-1-amd64 #1 SMP Sun Dec 11 20:36:41 UTC 2011 x86_64 GNU/Linux This is running on an Lenovo Thinkpad X201.