The invalid code below gives an "undefined reference" linker error on GCC 4.0.1 at -O0, but not at - O1; GCC 3.3.4 gives an error at both optimizations. This may not be a bug, if the version 4 optimizer is being cleverer than the version 3 optimizer; but the failure to reject the invalid code might be considered a regression. //By Stuart A. Malone, tweaked by Flash Sheridan #include <stdio.h> #include <stdint.h> class Foo { public: static const uint16_t kErrorCmd = 42; }; static uint32_t TestCmd(const uint16_t & cmd) { return (cmd == 42) ? 17 : 0; } int main() { printf("%u", TestCmd(Foo::kErrorCmd) ); } ----------- Here's the correct rejection: 368> /opt/gcc401chk/bin/g++ ../cpp/noerror/Llamagrahpics_static_constant_by_ref.cpp /tmp/cc3Hoo7z.o(.text+0x47): In function `main': : undefined reference to `Foo::kErrorCmd' collect2: ld returned 1 exit status Here's the full session for the failure to reject: 369> /opt/gcc401chk/bin/g++ -O1 -v ../cpp/noerror/Llamagrahpics_static_constant_by_ref.cpp Using built-in specs. Target: i686-pc-linux-gnu Configured with: ../configure --enable-checking --prefix=/opt/gcc401chk --enable-languages=c,c+ + Thread model: posix gcc version 4.0.1 /opt/gcc401chk/libexec/gcc/i686-pc-linux-gnu/4.0.1/cc1plus -quiet -v -D_GNU_SOURCE ../cpp/ noerror/Llamagrahpics_static_constant_by_ref.cpp -quiet -dumpbase Llamagrahpics_static_constant_by_ref.cpp -mtune=pentiumpro -auxbase Llamagrahpics_static_constant_by_ref -O1 -version -o /tmp/ccBQBEWy.s ignoring nonexistent directory "/opt/gcc401chk/lib/gcc/i686-pc-linux-gnu/4.0.1/../../../../i686-pc- linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /opt/gcc401chk/lib/gcc/i686-pc-linux-gnu/4.0.1/../../../../include/c++/4.0.1 /opt/gcc401chk/lib/gcc/i686-pc-linux-gnu/4.0.1/../../../../include/c++/4.0.1/i686-pc-linux-gnu /opt/gcc401chk/lib/gcc/i686-pc-linux-gnu/4.0.1/../../../../include/c++/4.0.1/backward /usr/local/include /opt/gcc401chk/include /opt/gcc401chk/lib/gcc/i686-pc-linux-gnu/4.0.1/include /usr/include End of search list. GNU C++ version 4.0.1 (i686-pc-linux-gnu) compiled by GNU C version 3.3.4 (pre 3.3.5 20040809). GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096 as -V -Qy -o /tmp/ccgiUdjh.o /tmp/ccBQBEWy.s GNU assembler version 2.15.91.0.2 (i586-suse-linux) using BFD version 2.15.91.0.2 20040727 (SuSE Linux) /opt/gcc401chk/libexec/gcc/i686-pc-linux-gnu/4.0.1/collect2 --eh-frame-hdr -m elf_i386 - dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o /opt/gcc401chk/lib/gcc/i686-pc- linux-gnu/4.0.1/crtbegin.o -L/opt/gcc401chk/lib/gcc/i686-pc-linux-gnu/4.0.1 -L/opt/gcc401chk/ lib/gcc/i686-pc-linux-gnu/4.0.1/../../.. /tmp/ccgiUdjh.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /opt/gcc401chk/lib/gcc/i686-pc-linux-gnu/4.0.1/crtend.o /usr/lib/crtn.o flash@thrallis scripts 21:09:40 370>
Created attachment 9489 [details] Llamagrahpics_static_constant_by_ref.cpp
Here's the discussion in our developer forum about the validity of this code; the rejection was originally reported as a bug against our compiler. At 4:34 PM -0500 2/16/04, Stuart A. Malone wrote: >But when I compile this kind of code using the native compiler, the >linker complains that Foo::kVersionNumber is an undefined symbol. >If I try to mollify it by placing code in my .cpp file like this: > > const int16_t Foo::kVersionNumber = 3; > >The compiler complains that the symbol has been defined twice. > >So how do I win? I checked a reference manual[1] last night, which said that the definition should be: const int16_t Foo::kVersionNumber; Keep the "= 3" in the class definition, like you did before. All you're doing with the above line is telling the compiler and linker where the storage should be defined. -- Keith Rollin -- Development Tools engineer [1] "The C Programming Language", Special Edition, p. 249, section 10.4.6.2, "Member Constants", where it says "If (and only if) you use an initialized member in a way that requires it to be stored as an object in memory, the member must be (uniquely) defined somewhere. The initializer may not be repeated: <example>".
Since the static const can be "inlined" at higher level of optimizations which is allowed by the C++ standard, this is not a bug.
*** Bug 26597 has been marked as a duplicate of this bug. ***