1

So I've been banging my head on this compiler error for the last 2 hours and thought I would post the code here to see if anyone can shed any light on my mistake.

I have stripped out all the irrelevant bits to leave a bare minimal program (shown below) which as far as I can see should compile and run. If I comme but I can't see what is wrongnt out the call to testFunc in main then everything compiles and runs fine. With the call to testFunc in however, I get the following:

$ ./waf -v --run abr-tool
Waf: Entering directory `/home/conor/workspace/msc/AdaptiveIPTV/Software/conor/ns3/ns-3.15/build'
[1665/1822] cxxprogram: build/src/abr-tools/examples/abr-tool.cc.4.o -> build/src/abr-tools/ns3.15-abr-tool-debug
19:04:19 runner ['/usr/bin/g++', '-L/usr/lib', '-lboost_iostreams', '-L/usr/lib', '-lboost_iostreams', '-pthread', 'src/abr-tools/examples/abr-tool.cc.4.o', '-o', '/home/conor/workspace/msc/AdaptiveIPTV/Software/conor/ns3/ns-3.15/build/src/abr-tools/ns3.15-abr-tool-debug', '-Wl,-Bstatic', '-Wl,-Bdynamic', '-Wl,--no-as-needed', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-lns3.15-point-to-point-debug', '-lns3.15-internet-debug', '-lns3.15-mpi-debug', '-lns3.15-bridge-debug', '-lns3.15-network-debug', '-lns3.15-core-debug', '-lrt']
src/abr-tools/examples/abr-tool.cc.4.o: In function `main':
/home/conor/workspace/msc/AdaptiveIPTV/Software/conor/ns3/ns-3.15/build/../src/abr-tools/examples/abr-tool.cc:7: undefined reference to `testFunc()'
collect2: ld returned 1 exit status

As you can see the code below is being built as part of a much larger project, and I am aware that the error may be coming from that build process rather than an issue with my code, but either way I have hit something of a wall in my understanding of what is happening here. I'm learning c++ as I go and to tell the truth I don't feel experienced enough to even just compile this code on its own and be able to say "that should definitely work but it doesn't", which is why I present it like this.

Another couple of points which might be relevant:

  • I can use macros defined in abr-helper.h from abr-tools.cc, and the problem persists when I put abr-tools.cc in the same folder as abr-helper.h and just use '#include "abr-helper.h"'.

  • the original error was the same thing, but for a bunch of other stuff defined in abr-helper.h and use in abr-tools.cc

I would appreciate any help you folks can offer, thanks in advance.

abr-helper.h:

#ifndef ABR_HELPER_H
#define ABR_HELPER_H
#include <iostream>

void testFunc();

#endif /* ABR_HELPER_H */

abr-helper.cc:

#include <iostream>
#include "abr-helper.h"

void testFunc(){
        std::cout << "this is all testFunc() does ..." << std::endl;
}

abr-tool.cc:

#include <iostream>
#include "ns3/abr-helper.h"

int main (int argc, char *argv[]){

    std::cout << "in main()" << std::endl;
    testFunc();
    return 0;

}
Tristram Gräbener
  • 9,601
  • 3
  • 34
  • 50

4 Answers4

5

It appears the file abr-helper.cc doesn't get compiled. You can easily test this by adding a

#error "Test"

line to that file. If the build succeeds, the file isn't getting compiled and you need to add it. How you do that depends on your compiler or IDE.

Luchian Grigore
  • 253,575
  • 64
  • 457
  • 625
  • I got it, thanks. abr-helper.cc was being compiled, but not linked when abr-tool.cc was compiled. It was configuration issue with the build tool. –  Dec 24 '12 at 21:58
1

You need to include abr-helper.cc in your compilation, otherwise the implementation is not linked in.

pbhd
  • 4,384
  • 1
  • 20
  • 26
1

I don't know waf, so I won't be able to give a solution. But here is what happens :

During compilation, everything works fine. The problem occurs during the linking (ld error).

On the line starting with : 19:04:19 runner, there is no reference to abr-helper.o or something like that. You must have forgotten to add abr-helper.cc somewhere in your waf configuration.

Tristram Gräbener
  • 9,601
  • 3
  • 34
  • 50
0

Additionally to the other answers (I also don't see the file abr-tool.cc to be compiled), the function void testFunc needs to be declared extern.

Josef Meixner
  • 161
  • 3
  • thanks, I read that it is only required for data and not functions. Is there still some issue with reliability if it isn't used, or just for correctness? –  Dec 24 '12 at 22:05
  • It is, but I have made it a habit to always write it. First it is valuable documentation and there is one case, when move the declaration of a former static function into a header it will catch if you forgot to remove the static from the definition. So I should probably take back the "needs" and substitute it with a "should". – Josef Meixner Dec 25 '12 at 11:28