The Dreaded "Unresolved External Symbol" :-(

This is a discussion on The Dreaded "Unresolved External Symbol" :-( within the C++ Programming forums, part of the General Programming Boards category; I was walking myself through an online tutorial on how to use the WinpCap library, and downloaded the first sample ...

  1. #1
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    The Dreaded "Unresolved External Symbol" :-(

    I was walking myself through an online tutorial on how to use the WinpCap library, and downloaded the first sample code sniplet. I compiled and that worked out fine, but when I tried to build I'm getting the following error:

    Linking...
    main.obj : error LNK2001: unresolved external symbol "int __cdecl pcap_findalldevs_ex(char *,struct pcap_rmtauth *,struct pcap_if * *,char *)" (?pcap_findalldevs_ex@@YAHPADPAUpcap_rmtauth@@PAPA Upcap_if@@0@Z)
    Debug/Get Adapter list.exe : fatal error LNK1120: 1 unresolved externals
    Error executing link.exe.

    I'm guessing this is coming from this first few lines in the sample program:

    Code:
        /* Retrieve the device list from the local machine */
        if (pcap_findalldevs_ex(PCAP_SRC_IF_STRING, NULL /* auth is                          not needed */, &alldevs, errbuf) == -1)
        {
            fprintf(stderr,"Error in pcap_findalldevs_ex: %s\n", errbuf);
            exit(1);
        }
    The function pcap_findalldevs_ex being the culprit.

    I'm using VC++ v6.0, and I have the WinpCap library installed in my libraries directory, as well as having it included in my project settings. Under the options menu in VC++ I've included all the proper directories pointing to the header & source files that came with the WinpCap source download.

    I even went so far as to look up the function pcap_findalldevs_ex in the online documention for WinpCap library, and found out in which header file it'ss defined, as well as in which .c file it's implemented. Both of these files are in my include & source directories.

    So, VC++ is complaining about an unresolved external symbol, basically telling me "your function implentation doesn't exist", when I know damn well that it DOES exist, because I've seen it.

    Any ideas?

    cheers,
    DrMario

  2. #2
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    An unresolved external symbol usually means that you have a declaration of a class or function in an external header file, but it's never defined anywhere. It means that you have something incomplete or awry with your external header files that are to be linked to your main source file.

  3. #3
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    > I'm using VC++ v6.0, and I have the WinpCap library installed in my libraries directory
    As well as saying where everything was, did you actually tell it the name of the library as well?

    In the "use additional libraries", you need the actual names of the libraries you want to link against.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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