error LNK2019: unresolved external symbol opencv

Question

I wrote this simple program that loads matrices from txt files and calculate distances. When compiling the program in visual studio on windows I get the following errors:

1>main.obj : error LNK2019: unresolved external symbol "void __cdecl cv::fastFree(void *)" (?fastFree@cv@@YAXPAX@Z) referenced in function "public: __thiscall     cv::Mat::~Mat(void)" (??1Mat@cv@@QAE@XZ)
1>system.obj : error LNK2001: unresolved external symbol "void __cdecl cv::fastFree(void *)" (?fastFree@cv@@YAXPAX@Z)
1>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall cv::Mat::deallocate(void)" (?deallocate@Mat@cv@@QAEXXZ) referenced in function "public: void __thiscall cv::Mat::release(void)" (?release@Mat@cv@@QAEXXZ)
1>system.obj : error LNK2001: unresolved external symbol "public: void __thiscall cv::Mat::deallocate(void)" (?deallocate@Mat@cv@@QAEXXZ)
1>main.obj : error LNK2019: unresolved external symbol "int __cdecl cv::_interlockedExchangeAdd(int *,int)" (?_interlockedExchangeAdd@cv@@YAHPAHH@Z) referenced in function "public: void __thiscall cv::Mat::release(void)" (?release@Mat@cv@@QAEXXZ)
1>system.obj : error LNK2001: unresolved external symbol "int __cdecl cv::_interlockedExchangeAdd(int *,int)" (?_interlockedExchangeAdd@cv@@YAHPAHH@Z)
1>system.obj : error LNK2019: unresolved external symbol "public: __thiscall cv::Exception::Exception(int,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,int)" (??0Exception@cv@@QAE@HABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@00H@Z) referenced in function "public: int & __thiscall cv::Mat::at<int>(int,int)" (??$at@H@Mat@cv@@QAEAAHHH@Z)
1>system.obj : error LNK2019: unresolved external symbol "public: virtual __thiscall cv::Exception::~Exception(void)" (??1Exception@cv@@UAE@XZ) referenced in function "public: int & __thiscall cv::Mat::at<int>(int,int)" (??$at@H@Mat@cv@@QAEAAHHH@Z)
1>system.obj : error LNK2019: unresolved external symbol "void __cdecl cv::error(class cv::Exception const &)" (?error@cv@@YAXABVException@1@@Z) referenced in function "public: int & __thiscall cv::Mat::at<int>(int,int)" (??$at@H@Mat@cv@@QAEAAHHH@Z)
1>system.obj : error LNK2019: unresolved external symbol "public: void __thiscall cv::Mat::create(int,int const *,int)" (?create@Mat@cv@@QAEXHPBHH@Z) referenced in function "public: void __thiscall cv::Mat::create(int,int,int)" (?create@Mat@cv@@QAEXHHH@Z)
1>C:\Users\Ram\documents\visual studio 2012\Projects\descrip\Debug\descrip.exe : fatal error LNK1120: 7 unresolved externals

I intsalled opencv 2.4.6 on my computer and linked it to visual studio properly.

main.cpp

#include "system.h"

using namespace std;

int main(int argc, char* argv[]){    
  if(argc != 3){
    cout << "Not enough arguments" << endl;
    exit(-1);
  }

  System s(argv[2]);
  s.Parse_Centers(argv[1]);
  s.Run();
  return 0;
} 

system.h

#include <iostream>
#include <fstream>
#include <dirent.h> 
#include <time.h>
#include "cv.h"
#include "highgui.h"
#include "opencv2/opencv.hpp"

#define NUM_CENTERS 5000
#define NUM_COL 512

using namespace cv;

class System{
public:
    System(char *dir);
    void Run();
    void Parse_Centers(char* path);
    void Compute_Histogram(const char* filename);

private:
    Mat centers;
    Mat centers_zero;
    char *dir_path;
};

system.cpp

#include "system.h"

using namespace std;
using namespace cv;

System::System(char *dir){
    centers.create(NUM_CENTERS, NUM_COL, CV_8U);
    centers_zero.create(NUM_CENTERS, NUM_COL, CV_8U);
    dir_path = dir;
};

void System::Parse_Centers(char* path){
    ifstream fin;
    int temp, n, line = 0;
    fin.open(path);

    if(!fin.good()){ 
        throw 1; 
    }

    while(!fin.eof()){
        char buf[2048];
        const char* token[NUM_COL] = {};

        n = 0;
        fin.getline(buf, 2048);
        token[0] = strtok(buf, ",");

        if(token[0]){
            temp = atoi(token[0]);
            if(temp){
                centers.at<int>(line,n) = temp;
                centers_zero.at<int>(line,n) = temp * temp;
            }

            for(int n = 1; n < 512; n++){
                token[n] = strtok(0, ",");
                temp = atoi(token[n]);
                if(temp){
                    centers.at<int>(line,n) = temp;
                    centers_zero.at<int>(line,n) = temp * temp;
                }
            }
        }
        line++;
    }

    fin.close();
};  

void System::Run(){
    DIR *dir;
    struct dirent *entry;
    time_t start_t;
    time_t end_t;

    dir = opendir(dir_path);
    if(!dir){
        cout << "Directory wasn't found" << endl;
        throw 3;  
    }

    while((entry = readdir(dir)) != NULL){
        if(entry->d_name[0] != '.'){
            string path = string(dir_path) + "/" + string(entry->d_name);
            cout << "entry: " << path;
            time(&start_t);
            Compute_Histogram(path.c_str());
            time(&end_t);
            cout << "   " << difftime(start_t,end_t) << "sec" << endl;
        }
    }

    closedir(dir);
}

void System::Compute_Histogram(const char* filename){
    int dist[NUM_CENTERS];
    int desc[NUM_CENTERS] = {0};
    int temp, place = 0;

    ifstream fin;
    fin.open(filename);

    if(!fin.good()){ 
        throw 2; 
    }

    while(!fin.eof()){
        char buf[2048];
        const char* token[512] = {};

        fin.getline(buf, 2048);
        token[0] = strtok(buf, ",");
        if(token[0]){
            temp = atoi(token[0]);
            if(temp){
                for(int i = 0; i < NUM_CENTERS; i++){
                    dist[i] = (temp - centers.at<int>(i,0)) * (temp - centers.at<int>(i,0));
                }
            }
            else{
                for(int i = 0; i < NUM_CENTERS; i++){  
                    dist[i] = centers_zero.at<int>(i,0);
                }
            }

            for(int n = 1; n < NUM_COL; n++){
                token[n] = strtok(0, ",");
                temp = atoi(token[n]);

                if(temp){
                    for(int i = 0; i < NUM_CENTERS; i++){
                        dist[i] += (temp - centers.at<int>(i,n)) * (temp - centers.at<int>(i,n));
                        if((n == 511) && (i > 0)){
                            if(dist[i] < dist[place]){
                                place = i;
                            }
                        }
                    }
                }
                else{
                    for(int i = 0; i < NUM_CENTERS; i++){
                        dist[i] += centers_zero.at<int>(i,n);
                        if((n == 511) && (i > 0)){
                            if(dist[i] < dist[place]){
                                place = i;
                            }
                        }
                    }
                }
            }
        }

        desc[place]++;
    }

    fin.close();

    ofstream outfile;
    string path;
    path = string(filename) + ".csv";
    outfile.open(path.c_str());
    for(int i = 0; i < 4999; i++){
        outfile << desc[i] << ",";
    }
    outfile << desc[4999];
    outfile.close();
};

What am i doing wrong????

Answer 1

Like others mentioned, you need to make sure you're linking to the OpenCV libs correctly.

Check that your Project -> Properties -> VC++ Directories -> Library Directories , includes the path where the OpenCV libraries are, the default would be 'C:\\opencv\\build\\x86\\vc11\\lib' (on a 32-bit machine running VS2012, it will vary on other setups).

Next, check that the following libraries are included in your Project -> Properties -> Linker -> Input -> Additional Dependencies :

opencv_core246d.lib
opencv_imgproc246d.lib
opencv_highgui246d.lib
opencv_ml246d.lib
opencv_video246d.lib
opencv_features2d246d.lib
opencv_calib3d246d.lib
opencv_objdetect246d.lib
opencv_contrib246d.lib
opencv_legacy246d.lib
opencv_flann246d.lib

If the above are correct, you shouldn't get any more OpenCV link errors.

Answer 2

Perhaps you are building for win32 but linking to x64. If you set your application to x64 then it will build, whereas in win32 it gives linking errors. Right click on the solution and go to configuration, platform column. I found it tricky to set this, I wonder if it's buggy or not.

Answer 3

Follow the steps to solve it

• Go to Project right click and select settings->C++->General->Additional include directories click edit and add this C:\\opencv\\build\\include.

• Now go to settings->Linker->General->Additional library Directories and paste C:\\opencv\\build\\x64\\vc15\\lib

• Now go to settings->Linker->Input and paste opencv_world343.lib,opencv_world343d.lib that is all,but these settings are true for visual studio 2017 and OpenCV 3.4.3 only for other versions will have to change accordingly.

Answer 4

All of the answers point in the right direction but I want to update what RedFred answered to the latest build as of today (4.0.0), change the libraries he mentioned for:

opencv_core400d.lib
opencv_imgproc400d.lib
opencv_highgui400d.lib
opencv_ml400d.lib
opencv_video400d.lib
opencv_features2d400d.lib
opencv_calib3d400d.lib
opencv_objdetect400d.lib
opencv_flann400d.lib

For next or previous builds just go to your lib folder in your opencv's directory and search for each of the items in the list that RedFred or I provided (obviously copy and paste only up to the last letter before the version number, in my case 400) and create your own additional dependencies list for your linker.

By the way I had to create my Visual Studio .sln from the source code using CMake, build with VS, then for some reason with the source came no include files so I added them to my include directories from the Win pack .

Answer 5

任何其他人如果只用几个未解析的外部符号opencv_world450d.lib这个问题，请注意在构建 Debug 时应该链接opencv_world450.lib在构建 Release 时应该链接opencv_world450.lib 。

Answer 6

You probably included the right header files, but forgot to add the library. You need to add the corresponding *.lib file in the project settings.

Answer 7

I got the problem by following the opencv tutorials. I fixed it by adding opencv_world450d.lib after adding opencv_world450.lib in Propeties-General-Linker-Input-Additional Dependancies.

Answer 8

For my case, I could not remove _interlockedExchangeAdd link error no matter how configure include/library path, and library file on my visual studio solution.

So I created new visual studio solution and added include/library path, library input files(opencv_world440.lib). With this, I could build the solution.

My previous solution had may sub projects inside the solution, so there might be some issue with solution configuration which I could not figure out.

One more thing, for debug build, you should use debug library(opencv_world440.lib)