undefined reference when linking with a c library from c++ code

[tfa...@chromium.org]

Hi,

I'm getting this in my sample application:

$ ninja -C out/Default/

ninja: Entering directory `out/Default/'

[2/2] LINK example_cpp

FAILED: clang++  -o example_cpp -Wl,--start-group obj/example_cpp.example_cpp.o obj/liblinenoise.a  -Wl,--end-group 

obj/example_cpp.example_cpp.o: In function `main':

../../example_cpp.cc:(.text+0x18): undefined reference to `linenoise(char const*)'

clang: error: linker command failed with exit code 1 (use -v to see invocation)

ninja: build stopped: subcommand failed.

Anyone knows why is that? What am I missing?

I attached the two files to demonstrate the failure. The rest of the code you can see at github.com/tfarina/cmdline-history

[tfa...@chromium.org]

the right link to the repo is github.com/tfarina/cmdline_history

[Evan Martin]

It looks like Ami helped you out (for the list: the problem was C++ name mangling).

One way to have diagnosed this is to compare the symbols needed by your example object against the symbols exported by your linenoise object.

Try temporarily undoing your 'extern C' bit to produce the error again, then run these commands:

$ nm out/Default/obj/linenoise.linenoise.o | grep linenoise

=> should produce ouput including something like this:

0000000000001b36 T linenoise

$ nm out/Default/obj/example_cpp.example_cpp.o | grep linenoise

=> should produce ouput including something like this:

                 U _Z9linenoisePKc

Then try running "c++filt" and pasting the second one in:

$ c++filt

                 U _Z9linenoisePKc

It will print

                 U linenoise(char const*)

which is the unmangled name (and the one printed in your error message).

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