Linker Error while linking .lib files "nresolved external symbol"
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Thread: Linker Error while linking .lib files "nresolved external symbol"

  1. #1
    Join Date
    Feb 2011
    Posts
    9

    Linker Error while linking .lib files "nresolved external symbol"

    Hi guys,

    I have project named TestingDLL(Win32 DLL project). It has the following header file

    (The code has been taken from a site which I dont remember but for discussion purpose this is fine)
    sampledll.h
    ---------------
    #ifndef INDLL_H
    #define INDLL_H

    #ifdef EXPORTING_DLL
    extern __declspec(dllexport) void HelloWorld() ;
    #else
    extern __declspec(dllimport) void HelloWorld() ;
    #endif
    #endif

    and a .cpp file
    sampldll.cpp
    ---------------
    #define EXPORTING_DLL
    #include "sampledll.h"
    #include <stdio.h>

    void HelloWorld()
    {
    printf("hello");
    }


    I have build this project and I got the TestingDLL.lib sucessfully after the build.

    I have another project CallingDLL(Win 32 Console application) whose code is as follows
    calling.cpp
    --------------
    #include "sampledll.h"
    #pragma comment(lib,"TestingDLL.lib")
    int main()
    {
    HelloWorld();
    return 0;
    }

    this code calls the library function Helloworld(). Now I went to projects->settings->link->input
    and specified the .lib file name and the path to find it. I also made chages in C/C++->preprocessor->Additional include directories and added the path where sampledll.h is found.

    I always get

    compiling...
    calling.cpp
    Linking...
    calling.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) void __cdecl HelloWorld(void)" (__imp_?HelloWorld@@YAXXZ)
    Debug/CallingDll.exe : fatal error LNK1120: 1 unresolved externals
    Error executing link.exe.

    CallingDll.exe - 2 error(s), 0 warning(s)

    I have also tried some other ways like going to tools->options->Directories and adding the paths but still I get the same error.

    It would be great help if someone tells me in a systematic manner on how to link a .lib file to another project.

    Thanks

  2. #2
    Join Date
    Nov 2003
    Location
    Belgium
    Posts
    8,062

    Re: Linker Error while linking .lib files "nresolved external symbol"


  3. #3
    Join Date
    Jul 2009
    Location
    India
    Posts
    835

    Re: Linker Error while linking .lib files "nresolved external symbol"

    seems to be you did it in correct manner, may be you missing proper path.. check all settings once again..

  4. #4
    VictorN's Avatar
    VictorN is offline Super Moderator Power Poster
    Join Date
    Jan 2003
    Location
    Wallisellen (ZH), Switzerland
    Posts
    17,545

    Re: Linker Error while linking .lib files "nresolved external symbol"

    When DLL (und lib) is created (compiled( the EXPORTING_DLL is defined. So the type of the HelloWorld() is
    Code:
    extern __declspec(dllexport) void HelloWorld() ;
    But if EXPORTING_DLL is not defined in exe project then HelloWorld() would be declared as
    Code:
    extern __declspec(dllimport) void HelloWorld() ;
    And it seems to be the case here: the linker in exe project looks for "__declspec(dllimport) void __cdecl HelloWorld(void)" while the lib contains only "__declspec(dllexport) void __cdecl HelloWorld(void)"
    Victor Nijegorodov

  5. #5
    Join Date
    Feb 2011
    Posts
    9

    Re: Linker Error while linking .lib files "nresolved external symbol"

    Hi guys
    thanks for the replies. I havent got rid of the previous problem but I tried a new toy project to understand the linking. It is as follows

    code for dll
    example.cpp
    ---------------

    / Example.cpp : Defines the entry point for the DLL application.
    //

    #include "stdafx.h"

    // This function is used to calculate the total area of a parallelepiped rectangle
    double BoxArea(double L, double H, double W);
    // This function is used to calculate the volume of a parallelepiped rectangle
    double BoxVolume(double L, double H, double W);
    // This function is used to get the dimensions of a rectangular parallelepiped
    // calculate the area and volume, then pass the calculated values to the
    // function that called it.
    extern "C" __declspec(dllexport)void BoxProperties(double Length, double Height,
    double Width, double& Area, double& Volume);

    BOOL APIENTRY DllMain( HANDLE hModule,
    DWORD ul_reason_for_call,
    LPVOID lpReserved
    )
    {
    return TRUE;
    }

    double BoxArea(double L, double H, double W)
    {
    return 2 * ((L*H) + (L*W) + (H*W));
    }

    double BoxVolume(double L, double H, double W)
    {
    return L * H * W;
    }

    void BoxProperties(double L, double H, double W, double& A, double& V)
    {
    A = BoxArea(L, H, W);
    V = BoxVolume(L, H, W);
    }

    I build the project and there were no errors and I got the .lib and .dll files upon building the project.

    There is another project where I am trying to use the .lib generated above. I have copied the Example.lib, Example.dll and Example.obj to the new project folder . I also added these files to the project. In the project->settings->link->input I appended Example.lib to the Object/Library module text box . I wrote the following cpp code in the new project.
    test.cpp
    -----------
    #include <iostream>

    extern "C" __declspec(dllimport)void BoxProperties(double L, double H,
    double W, double& A, double& V);

    int main()
    {
    double Length, Height, Width, Area, Volume;

    cout << "Enter the dimensions of the box\n";
    cout << "Length: ";
    cin >> Length;
    cout << "Height: ";
    cin >> Height;
    cout << "Width: ";
    cin >> Width;

    BoxProperties(Length, Height, Width, Area, Volume);

    cout << "\nProperties of the box";
    cout << "\nLength: " << Length;
    cout << "\nHeight: " << Height;
    cout << "\nWidth: " << Width;
    cout << "\nArea: " << Area;
    cout << "\nVolumne: " << Volume;

    cout << "\n\n";

    return 0;
    }

    After building the code I get the following linker error(no previous linker errors ):

    --------------------Configuration: Exampletest - Win32 Debug--------------------
    Linking...
    Creating library Debug/Exampletest.lib and object Debug/Exampletest.exp
    LIBCMTD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
    Debug/Exampletest.exe : fatal error LNK1120: 1 unresolved externals
    Error executing link.exe.

    Exampletest.exe - 2 error(s), 0 warning(s)

    Guys help me resolve this

    Thanks

  6. #6
    VictorN's Avatar
    VictorN is offline Super Moderator Power Poster
    Join Date
    Jan 2003
    Location
    Wallisellen (ZH), Switzerland
    Posts
    17,545

    Re: Linker Error while linking .lib files "nresolved external symbol"

    Please, edit your post adding Code tags around code snippets. Otherwise your code is absolutely unreadable!
    Victor Nijegorodov

  7. #7
    Join Date
    Feb 2011
    Posts
    9

    Re: Linker Error while linking .lib files "nresolved external symbol"

    Thanks for the suggestion Victor! I will take care of that in my future posts.

    Well thanks for all the help you guys have done. I finally resolved my issues regarding linker error. I will update this post with step by step procedure I figured out to make a dll and use it in other applications.

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