I have a C++ library and a C++ application trying to use functions and classes exported from the library. The library builds fine and the application compiles but fails to link. The errors I get follow this form:
app-source-file.cpp:(.text+0x2fdb): undefined reference to `lib-namespace::GetStatusStr(int)’
Classes in the library seem to be resolved just fine by the linker, but free functions and exported data (like a cosine lookup table) invariably result in the above error.
I am using Ubuntu 8.04 (Hardy), and it is up to date with the latest Ubuntu packages.
The command to link the library is (with other libraries removed):
g++ -fPIC -Wall -O3 -shared -Wl,-soname,lib-in-question.so -o ~/project/lib/release/lib-in-question.so
The command to link the application is (with other libraries removed):
g++ -fPIC -Wall -O3 -L~/project/lib/release -llib-in-question -o ~/project/release/app-in-question
Finally, it appears (as best as I can tell) that the symbols in question are being exported properly:
nm -D ~/project/lib/release/lib-in-question.so | grep GetStatusStr --> U _ZN3lib-namespace12GetStatusStrEi
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Answer
the U before _ZN3lib-namespace12GetStatusStrEi in the nm output shows that the symbol is undefined in the library.
Maybe it’s defined in the wrong namespace: it looks like you’re calling it in lib-namepace but you might be defining it in another.