compilation error of OpenCV cpp code using Qt - c++

Question

I am using a very basic OpenCV code to compile using Qt but every time the following errors are coming.
OpenCV version
OpenCV version : 3.4.3
Major version : 3
Minor version : 4
Subminor version : 3
My code
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include "opencv2/imgproc/imgproc_c.h"
#include "opencv2/imgproc/imgproc.hpp"
using namespace std;
using namespace cv;
int main()
{
Mat I = imread("path/filename.ppm", 1);
imshow("conv_image",I);
waitKey();
return 0;
}
.pro file
QT -= gui
CONFIG += c++11 console
CONFIG -= app_bundle
# The following define makes your compiler emit warnings if you
use
# any feature of Qt which as been marked deprecated (the exact
warnings
# depend on your compiler). Please consult the documentation of
the
# deprecated API in order to know how to port your code away from
it.
DEFINES += QT_DEPRECATED_WARNINGS
# You can also make your code fail to compile if you use
deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a
certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables
all the APIs deprecated before Qt 6.0.0
SOURCES += main.cpp
INCLUDEPATH += /usr/local/include/opencv
LIBS += -L/usr/local/lib -lopencv_core -lopencv_imgcodecs -
lopencv_highgui
Given Error
:-1: warning: libopencv_core.so.3.4, needed by /usr/local/lib/libopencv_imgcodecs.so, may conflict with libopencv_core.so.2.4
:-1: error: main.o: undefined reference to symbol '_ZN2cv6String10deallocateEv'
/usr/local/lib/libopencv_core.so.3.4:-1: error: error adding symbols: DSO missing from command line
:-1: error: collect2: error: ld returned 1 exit status
In my .pro file, I have used the following line(from the different link I have found 3 ways, I have tried all but failed)
First
INCLUDEPATH += /usr/local/include/opencv
LIBS += -L/usr/local/lib -lopencv_core -lopencv_imgcodecs -
lopencv_highgui
Second
INCLUDEPATH +=/usr/local/include/opencv
LIBS +=`pkg-config --libs opencv`
Third
I have used information from here
Please give me suggestion to solve the issue.