(OpenCV) Getting a 'unresolved external symbol' error

Question

I'm using this tutorial (from http://hxr99.blogspot.com/2011/12/opencv-examples-showing-image.html), but many errors show up:

#include <iostream>
#include <opencv2\opencv.hpp>

using namespace std;
using namespace cv;


int main( int argc, const char** argv )
{
    Mat image;
    String inputName;

    for( int i = 1; i < argc; i++ )
    {
            inputName.assign( argv[i] );
    }

    if( inputName.empty() || (isdigit(inputName.c_str()[0]) && inputName.c_str()[1] == '\0') )
    {
       if( inputName.size() )
    {
        image = imread( inputName, 1 );
    }
    else
    {
        if(image.empty()) cout << "Couldn't read image" << endl;
    }
    imshow("Test",image);
    }
}

Errors:

1>------ Build started: Project: Project1, Configuration: Debug x64 ------
1>  main.cpp
1>main.obj : error LNK2019: unresolved external symbol "void __cdecl cv::fastFree(void *)" (?fastFree@cv@@YAXPEAX@Z) referenced in function "public: __cdecl cv::Mat::~Mat(void)" (??1Mat@cv@@QEAA@XZ)
1>main.obj : error LNK2019: unresolved external symbol "public: __cdecl cv::_InputArray::_InputArray(class cv::Mat const &)" (??0_InputArray@cv@@QEAA@AEBVMat@1@@Z) referenced in function main
1>main.obj : error LNK2019: unresolved external symbol "public: void __cdecl cv::Mat::deallocate(void)" (?deallocate@Mat@cv@@QEAAXXZ) referenced in function "public: void __cdecl cv::Mat::release(void)" (?release@Mat@cv@@QEAAXXZ)
1>main.obj : error LNK2019: unresolved external symbol "public: void __cdecl cv::Mat::copySize(class cv::Mat const &)" (?copySize@Mat@cv@@QEAAXAEBV12@@Z) referenced in function "public: class cv::Mat & __cdecl cv::Mat::operator=(class cv::Mat const &)" (??4Mat@cv@@QEAAAEAV01@AEBV01@@Z)
1>main.obj : error LNK2019: unresolved external symbol "int __cdecl cv::_interlockedExchangeAdd(int *,int)" (?_interlockedExchangeAdd@cv@@YAHPEAHH@Z) referenced in function "public: class cv::Mat & __cdecl cv::Mat::operator=(class cv::Mat const &)" (??4Mat@cv@@QEAAAEAV01@AEBV01@@Z)
1>main.obj : error LNK2019: unresolved external symbol "void __cdecl cv::imshow(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class cv::_InputArray const &)" (?imshow@cv@@YAXAEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AEBV_InputArray@1@@Z) referenced in function main
1>main.obj : error LNK2019: unresolved external symbol "class cv::Mat __cdecl cv::imread(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,int)" (?imread@cv@@YA?AVMat@1@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@H@Z) referenced in function main
1>c:\users\gerard\documents\visual studio 2012\Projects\Project1\x64\Debug\Project1.exe : fatal error LNK1120: 7 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

I don't know what's happening. Any help is very very appreciated. Btw, I'm using Visual Studio 2012, and I (hope to) have the correct PATH and libraries.

Solution

I ran into a similar problem with OpenCV. You're likely missing one or more .lib files to the Linker.

You can add them by:

1. Right-Clicking on your project in Visual Studio.
2. Selecting "Properties"
3. Take note of: "Linker > General > Additional Library Directories"
4. Go to "Linker > Input > Additional Dependencies"

I specified OpenCV lib directory to VS under "Additional Library Directories". I browsed to this location and added my missing .lib files in "Additional Dependencies".

For example (I'm using 2.4.9 debug, so I added):

opencv_calib3d249d.lib
opencv_contrib249d.lib
opencv_core249d.lib
opencv_features2d249d.lib
opencv_flann249d.lib
opencv_gpu249d.lib
opencv_highgui249d.lib
opencv_imgproc249d.lib
opencv_legacy249d.lib
opencv_ml249d.lib
opencv_nonfree249d.lib
opencv_objdetect249d.lib
opencv_ocl249d.lib
opencv_photo249d.lib
opencv_stitching249d.lib
opencv_superres249d.lib
opencv_ts249d.lib
opencv_video249d.lib
opencv_videostab249d.lib

If you're using release, make sure to use only the release libs!

You might have to do something similar depending on how you setup your project.