Qt Creator Error: cannot find -lopencv_imgcodecs - c++

Question

I have installed opencv, qt, qt creator, cmake on ubuntu 15.10 through VMware on windows.
The opencv is installed in this directory: /home/majidalaeinia/opencv/
The project repository is cloned in this directory: /home/majidalaeinia/Desktop/imgwarp-opencv/
I want to run the project through its CMakeLists.txt in qt creator and when I press Build now on qt creator, I get the following errors:
error: cannot find -lopencv_imgcodecs
error: collect2: error: ld returned 1 exit status
Where is the problem and how can I solve it?

Answer 1

# Majid Alaeinia, from the CMakeLists.txt file you posted it is not specified how CMAKE should find the libraries requested from your project. Also there are no target_link_libraries declared so CMAKE does not know where to link them. Hopefully the following small example template should be helpful for your project:
cmake_minimum_required (VERSION 3.1)
project(yourProject)
find_package( OpenCV REQUIRED )
find_package( Qt5 REQUIRED COMPONENTS Sql )
### this is for c++11
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
set(CMAKE_INCLUDE_CURRENT_DIR ON)
### QT stuff if you want a GUI
set(CMAKE_AUTOMOC ON) # autogenerate qt gui features
set(CMAKE_AUTORCC ON) # used for QT resource Files (if you need)
## Additional operation...
# From here you are specifically linking all OpenCV libraries and executables
### Add executables
add_executable(yourExecutable main/main.cpp ui/res/res.qrc ${SRCS} ${UI_HDRS} ${UI_SRCS})
target_link_libraries (yourProject example Qt5::Widgets ${OpenCV_LIBS} Qt5::Sql)
### Add Library
add_library(yourProject_lib SHARED ${SRCS} ${UI_HDRS})
target_link_libraries (yourProject_lib example Qt5::Widgets ${OpenCV_LIBS})

Answer 2

# Majid Alaeinia,I uploaded the repository and went through the code. if you go inside the demo folder and you change the present CMakeLists.txt file with the one I provided below it should compile (It does compile on mine with the provided changes):
project(demo)
cmake_minimum_required(VERSION 2.6)
find_package(Qt5 REQUIRED COMPONENTS Widgets Core)
FIND_PACKAGE( OpenCV REQUIRED )
include_directories(${QT_INCLUDES} ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_SOURCE_DIR}/lib ${CMAKE_CURRENT_SOURCE_DIR})
set(demo_SRCS main.cpp projfile.cpp deformwin.cpp myimage.cpp singlephotoview.cpp pointspaint.cpp)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
set(CMAKE_INCLUDE_CURRENT_DIR ON)
#qt5_automoc(${demo_SRCS})
QT5_WRAP_CPP(QOBJ_CPP ${demo_SRCS})
qt5_wrap_ui(helloworld_FORMS_HEADERS deformwin.ui)
add_executable(demo ${demo_SRCS} ${helloworld_FORMS_HEADERS})
target_link_libraries(demo ${QT_QTCORE_LIBRARY} ${QT_QTGUI_LIBRARY} imgwarp-lib opencv_core opencv_imgproc opencv_imgcodecs)
The code in the repository is an old code and still carries Qt4 as main wrappers. I think you probably have Qt5 installed on your computer and in fact the code I provided it will work for Qt5. Use it as a guideline for the other CMakeLists.txt file present inside src folder and change accordingly.
CMake will compile but because it was used Qt4 you need to figure out the most important modules to add, for example the new standard for including QtGui/QApplication is usually substituted by QtWidgets/QApplication
I also wanted to leave my previous answer in case you need a starting point or a initial template. I hope this clarifies a bit more and can get you move forward for your project.