Qt-Creator中OpenCV程序中的链接器错误

Question

I get the following error in Qt-Creator, qt-5.4 with OpenCV-3 installation :-

:-1: error: LNK1104: cannot open file 'opencv_ts300.lib'

In my project's .pro file I have added -

INCLUDEPATH += "E:\opencv\build\include"

LIBS += -L"E:\opencv\build\x86\vc11\lib"
LIBS += -lopencv_ts300d \ -lopencv_world300d \ -lopencv_ts300 \   -lopencv_world300d

The following is my main.cpp program :-

#include "mainwindow.h"
#include <QApplication>
#include<opencv2/opencv.hpp>

using namespace cv; // else would have to specify cv::cvtColor() etc.


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

QApplication a(argc, argv);
MainWindow w;
w.show();
char * imageName ="2-dp.JPG" ; // read the name of image to be loaded called   3-dp.JPG

Mat image;                  // declare Mat type object to load image-matrix

image = imread(imageName,1); // image object now contains image-matrix of the image loaded

if(!image.data)  // if image-data was invalid/non-existent/could not be read
{
    printf("No image data to load \n"); // then print messg
    return -1;                          // and exit program with exit code -1
}

Mat gray_image;            // Mat object declared for the image after gray-scale conversion

cvtColor(image, gray_image, CV_BGR2GRAY); // converts from BGR/RGB color space to gray scale

/*imwrite ("Gray_Image.jpg",gray_image);*/ //writes image-data (converted to gray scale iamge) into disk in JPEG format at file path given

namedWindow(imageName,CV_WINDOW_AUTOSIZE); // creates a named window for original image s.t window auto-scales its size as per image
namedWindow("Gray Image",CV_WINDOW_AUTOSIZE);

imshow(imageName,image);    // displays the image on the namedWindow by giving name of namedWindow
imshow("Gray Image",gray_image);

waitKey(0); //waits forever till user presses key


return a.exec();
}

Please help!

Answer 1

Linkage

The backslash symbol \\ should not be used between library names in one line. It does not give the error message mentioned in the question, however linkage fails with the same error code.

The backslash symbol may be used to break long lines:

LIBS += -lopencv_ts300d \
        -lopencv_world300d

Otherwise the libraries should be listed in one line without \\ :

LIBS += -lopencv_ts300 -lopencv_world300

---

Runtime

There are few issues that may be revealed at runtime.

There are two library types: debug (marked by suffix d ) and release. They should not be mixed in one build. Using wrong library type may lead to runtime crash, for example OpenCV in Qt crashes on deallocation of vector of lines when using HoughLinesP

It is possible to write qmake .pro file that uses only proper libraries depending on release or debug mode:

INCLUDEPATH += "E:\opencv\build\include"

LIBS += -L"E:\opencv\build\x86\vc11\lib"

CONFIG(release, debug|release) {
    # release libraries
    LIBS += -lopencv_ts300 -lopencv_world300
}

CONFIG(debug, debug|release) {
    # debug libraries
    LIBS += -lopencv_ts300d \
            -lopencv_world300d
}

Note that there are also binary dynamic loaded libraries in E:\\opencv\\build\\x86\\vc11\\bin . If those libraries cannot be found at runtime the application should crash. That path may be added to the system PATH environment variable or required libraries may be copied to application folder or to other place listed in system PATH .

---

Make sure that you are using compiler, linker and Qt build for vc11 . For MSVC2013 the libraries from the folder vc12 ( E:\\opencv\\build\\x86\\vc12\\lib ) should be used.