Undefined references causing compilation to fail

Undefined references causing compilation to fail

Bob Keane

Member #7,342

June 2006

I downloaded some files to play with networking in c++ and tried to compile but get the following errors:

g++ -o simple_server ServerSocket.o Socket.o simple_server_main.o
simple_server_main.o: In function `main':
simple_server_main.cpp:(.text+0x4a): undefined reference to `ServerSocket::ServerSocket(int)'
simple_server_main.cpp:(.text+0x69): undefined reference to `ServerSocket::accept(ServerSocket&)'
simple_server_main.cpp:(.text+0x88): undefined reference to `ServerSocket::operator>>(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&) const'
simple_server_main.cpp:(.text+0x9b): undefined reference to `ServerSocket::operator<<(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) const'
simple_server_main.cpp:(.text+0xf2): undefined reference to `ServerSocket::~ServerSocket()'
simple_server_main.cpp:(.text+0x109): undefined reference to `ServerSocket::~ServerSocket()'
simple_server_main.cpp:(.text+0x11d): undefined reference to `ServerSocket::~ServerSocket()'
simple_server_main.o: In function `ServerSocket::ServerSocket()':
simple_server_main.cpp:(.text._ZN12ServerSocketC2Ev[_ZN12ServerSocketC5Ev]+0x1b): undefined reference to `vtable for ServerSocket'
collect2: error: ld returned 1 exit status
Makefile:11: recipe for target 'simple_server' failed
make: *** [simple_server] Error 1

I went to Ubuntu forums and they suggested adding #include <iostream> and the program will compile with warnings but it is not. My gcc version is gcc version 6.2.0 20161005 (Ubuntu 6.2.0-5ubuntu12). I'm thinking there is some version incompatibility, am I right? All files attached.

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Edgar Reynaldo

Major Reynaldo

May 2007

Linking order is important. You have to link dependent libraries ~~last~~ first. So link ServerSocket.o after server main.

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Bob Keane

Member #7,342

June 2006

Thanks for the help. It probably is something so simple.

bamccaig

Member #7,536

July 2006

Hmmm, if simple_server_main depends on ServerSocket I would expect the linker order to be as is... Unless maybe ServerSocket depended on Socket, but then the linker errors would be different... Did you build all of these objects yourself? Also, could you wrap the project into an archive so it's only a single attachment instead of many? (/me should modify acc.js to automatically do this using jszip)

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Edgar Reynaldo

Major Reynaldo

May 2007

If simple_server_main depends on ServerSocket, then ServerSocket has to be linked after simple_server_main so that the missing symbols in simple_server_main get linked in properly.

bamccaig

Member #7,536

July 2006

That's the opposite of how I thought it worked. Though I've found that certain platforms/linkers are more picky than others.

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I mean the best with what I say. It doesn't always sound that way.

Bob Keane

Member #7,342

June 2006

All good advice but the left hand/right hand frustration kicked in and I found references to ex_enet_server and ex_enet_client. Now if I can figure out why enet will not install...

Edgar Reynaldo

Major Reynaldo

May 2007

gcc's linker ld only makes a single pass when linking. MSVC lets you get away with it though, as they read all the libraries first and then perform linking.

Bob Keane

Member #7,342

June 2006

The program uses a make file to compile. Any ideas how to change the file or manually compile the programs to resolve the order?

bamccaig

Member #7,536

July 2006

Is the makefile static or generated? If it's static you can just open it in a text editor. If you don't know the makefile syntax that may not be entirely trivial, but they're just text files. You can probably figure it out or we can help. If it's generated then you may need to fix the source file(s) that generated it instead. Or you could settle for just fixing the generated makefile and having to manually fix it anytime you regenerate it...

Again, if you made it easier to download the files one of us might find ourselves motivated to try to build it. That might speed the process along. Alternatively, if you found this code somewhere online you could just refer us to there (I don't recall that coming up yet).

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I mean the best with what I say. It doesn't always sound that way.

Bob Keane

Member #7,342

June 2006

Hereis where I got the sources.