QT5在windows下调用OpenCV库出现: undefined reference to `xxxxx&#39; 错误解决办法（适用MinGW编译器）。

一、环境介绍

window系统：win10 X64

QT版本: 5.12

QT5.12自带的MinGW编译器版本：mingw730_32 与mingw730_64

在QT的安装目录下，可以查看MinGW编译器的版本:

QT5在windows下调用OpenCV库出现: undefined reference to `xxxxx&#39; 错误解决办法（适用MinGW编译器）。

二、使用OpenCV出现的问题

在QT框架代码里使用老版本的分类器(cvLoad、cvHaarDetectObjects)处理图像时，正常编译没有问题，当使用新版本级联分类器(CascadeClassifier)时，程序编译就会出现一堆没有定义的错误：

release/widget.o:widget.cpp:(.text+0x2a1): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text+0x465): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text+0x631): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text+0x63b): undefined reference to `cv::_OutputArray::_OutputArray(cv::Mat&)'
release/widget.o:widget.cpp:(.text+0x64b): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
release/widget.o:widget.cpp:(.text+0x66a): undefined reference to `cv::cvtColor(cv::_InputArray const&, cv::_OutputArray const&, int, int)'
release/widget.o:widget.cpp:(.text+0x6c9): undefined reference to `cv::Mat::copySize(cv::Mat const&)'
release/widget.o:widget.cpp:(.text+0x6de): undefined reference to `cv::Mat::copySize(cv::Mat const&)'
release/widget.o:widget.cpp:(.text+0x6f9): undefined reference to `cv::Mat::copySize(cv::Mat const&)'
release/widget.o:widget.cpp:(.text+0x786): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x796): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x7a4): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x7b3): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x7c6): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x7d4): more undefined references to `cv::Mat::deallocate()' follow
release/widget.o:widget.cpp:(.text+0x150b): undefined reference to `cv::_OutputArray::_OutputArray(cv::Mat&)'
release/widget.o:widget.cpp:(.text+0x151e): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
release/widget.o:widget.cpp:(.text+0x1540): undefined reference to `cv::cvtColor(cv::_InputArray const&, cv::_OutputArray const&, int, int)'
release/widget.o:widget.cpp:(.text+0x15e1): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text+0x15f2): undefined reference to `cv::_OutputArray::_OutputArray(cv::Mat&)'
release/widget.o:widget.cpp:(.text+0x1605): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
release/widget.o:widget.cpp:(.text+0x1627): undefined reference to `cv::cvtColor(cv::_InputArray const&, cv::_OutputArray const&, int, int)'
release/widget.o:widget.cpp:(.text+0x1634): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x23a9): undefined reference to `cv::CascadeClassifier::CascadeClassifier()'
release/widget.o:widget.cpp:(.text+0x23b4): undefined reference to `cv::CascadeClassifier::CascadeClassifier()'
release/widget.o:widget.cpp:(.text+0x23bf): undefined reference to `cv::CascadeClassifier::CascadeClassifier()'
release/widget.o:widget.cpp:(.text+0x2458): undefined reference to `cv::CascadeClassifier::load(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
release/widget.o:widget.cpp:(.text+0x24f5): undefined reference to `cv::CascadeClassifier::~CascadeClassifier()'
release/widget.o:widget.cpp:(.text+0x2500): undefined reference to `cv::CascadeClassifier::~CascadeClassifier()'
release/widget.o:widget.cpp:(.text+0x250b): undefined reference to `cv::CascadeClassifier::~CascadeClassifier()'
release/widget.o:widget.cpp:(.text+0x25af): undefined reference to `cv::CascadeClassifier::load(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
release/widget.o:widget.cpp:(.text+0x268f): undefined reference to `cv::CascadeClassifier::load(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
release/widget.o:widget.cpp:(.text+0x280a): undefined reference to `cv::Mat::create(int, int const*, int)'
release/widget.o:widget.cpp:(.text+0x28b1): undefined reference to `cv::_OutputArray::_OutputArray(cv::Mat&)'
release/widget.o:widget.cpp:(.text+0x28c8): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
release/widget.o:widget.cpp:(.text+0x28f3): undefined reference to `cv::cvtColor(cv::_InputArray const&, cv::_OutputArray const&, int, int)'
release/widget.o:widget.cpp:(.text+0x2907): undefined reference to `cv::_OutputArray::_OutputArray(cv::Mat&)'
release/widget.o:widget.cpp:(.text+0x291e): undefined reference to `cv::_InputArray::_InputArray(cv::Mat const&)'
release/widget.o:widget.cpp:(.text+0x2939): undefined reference to `cv::equalizeHist(cv::_InputArray const&, cv::_OutputArray const&)'
release/widget.o:widget.cpp:(.text+0x29cb): undefined reference to `cv::CascadeClassifier::detectMultiScale(cv::Mat const&, std::vector<cv::Rect_<int>, std::allocator<cv::Rect_<int> > >&, double, int, int, cv::Size_<int>, cv::Size_<int>)'
release/widget.o:widget.cpp:(.text+0x2aac): undefined reference to `cv::ellipse(cv::Mat&, cv::Point_<int>, cv::Size_<int>, double, double, double, cv::Scalar_<double> const&, int, int, int)'
release/widget.o:widget.cpp:(.text+0x2acc): undefined reference to `cv::Mat::Mat(cv::Mat const&, cv::Rect_<int> const&)'
release/widget.o:widget.cpp:(.text+0x2b61): undefined reference to `cv::CascadeClassifier::detectMultiScale(cv::Mat const&, std::vector<cv::Rect_<int>, std::allocator<cv::Rect_<int> > >&, double, int, int, cv::Size_<int>, cv::Size_<int>)'
release/widget.o:widget.cpp:(.text+0x2bf6): undefined reference to `cv::CascadeClassifier::detectMultiScale(cv::Mat const&, std::vector<cv::Rect_<int>, std::allocator<cv::Rect_<int> > >&, double, int, int, cv::Size_<int>, cv::Size_<int>)'
release/widget.o:widget.cpp:(.text+0x2cce): undefined reference to `cv::circle(cv::Mat&, cv::Point_<int>, int, cv::Scalar_<double> const&, int, int, int)'
release/widget.o:widget.cpp:(.text+0x2d90): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text+0x2ec0): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text+0x2f42): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text+0x2fc8): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text+0x3047): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x3057): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x3067): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x3077): undefined reference to `cv::Mat::deallocate()'
release/widget.o:widget.cpp:(.text+0x3094): undefined reference to `cv::CascadeClassifier::~CascadeClassifier()'
release/widget.o:widget.cpp:(.text+0x309f): undefined reference to `cv::CascadeClassifier::~CascadeClassifier()'
release/widget.o:widget.cpp:(.text+0x30aa): undefined reference to `cv::CascadeClassifier::~CascadeClassifier()'
release/widget.o:widget.cpp:(.text$_ZN2cv3MatD1Ev[__ZN2cv3MatD1Ev]+0x64): undefined reference to `cv::fastFree(void*)'
release/widget.o:widget.cpp:(.text$_ZN2cv3MatD1Ev[__ZN2cv3MatD1Ev]+0x71): undefined reference to `cv::Mat::deallocate()'
collect2.exe: error: ld returned 1 exit status
mingw32-make[1]: *** [Makefile.Release:71: release/qt_opencv.exe] Error 1
mingw32-make: *** [Makefile:38: release] Error 2
mingw32-make[1]: Leaving directory 'D:/linux-share-dir/QT/build-qt_opencv-Desktop_Qt_5_12_6_MinGW_32_bit-Release'
21:11:46: 进程"C:\Qt\Qt5.12.6\Tools\mingw730_32\bin\mingw32-make.exe"退出，退出代码 2 。
Error while building/deploying project qt_opencv (kit: Desktop Qt 5.12.6 MinGW 32-bit)
When executing step "Make"

三、解决办法

方法1: 使用当前QT使用的MinGW编译器，重新编译一份OpenCV的源码再使用。

方法2: 使用已经编译好的MinGW版本OpenCV库，直接调用。

既然已经有编译好的MinGW库，就不用麻烦自己再去编译了，各种OpenCV对应的MinGW编译器编译的库下载地址:

https://github.com/huihut/OpenCV-MinGW-Build

。

由于我的源代码里使用了OpenCV3.x和2.X版本的很多函数，在OpenCV4.X里已经不存在，为了兼容代码，我这里下载OpenCV3.X版本的库。

下载之后，将bin目录加到系统的环境变量PATH里，方便程序在运行时能够找到对应的动态库。

在QT的工程文件里加入OpenCV头文件的路径和库路径即可：

QT       += core gui
QT       += multimediawidgets
QT       += xml
QT       += multimedia
QT       += network
QT       += widgets
QT       += serialport
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
 
CONFIG += c++11
 
# The following define makes your compiler emit warnings if you use
# any Qt feature that has 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 it uses 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 \
    widget.cpp
 
HEADERS += \
    widget.h
 
FORMS += \
    widget.ui
 
# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target
 
#linu平台的路径设置
linux {
message('运行linu版本')
#添加opencv头文件的路径，需要根据自己的头文件路径进行修改
INCLUDEPATH+=/home/wbyq/work_pc/opencv-3.4.9/_install/install/include\
             /home/wbyq/work_pc/opencv-3.4.9/_install/install/include/opencv\
             /home/wbyq/work_pc/opencv-3.4.9/_install/install/include/opencv2
 
LIBS+=/home/wbyq/work_pc/opencv-3.4.9/_install/install/lib/libopencv_*
}
 
win32
{
    message('运行win32版本')
    #添加opencv头文件的路径，需要根据自己的头文件路径进行修改
    INCLUDEPATH+=C:/OpenCV_3.4.7/OpenCV-MinGW-Build-OpenCV-3.4.7/include \
                 C:/OpenCV_3.4.7/OpenCV-MinGW-Build-OpenCV-3.4.7/include/opencv \
                 C:/OpenCV_3.4.7/OpenCV-MinGW-Build-OpenCV-3.4.7/include/opencv2
    LIBS+=C:/OpenCV_3.4.7/OpenCV-MinGW-Build-OpenCV-3.4.7/x86/mingw/bin/libopencv_*.dll
}
 
RESOURCES += \
    image.qrc

清除之前编译报错的文件，再次编译即可。

QT5在windows下调用OpenCV库出现: undefined reference to `xxxxx&#39; 错误解决办法（适用MinGW编译器）。

继续阅读

Compile workrave under windows &ndash; My exprience 在Windows上编译Workrave

Windows下使用GSL（GNU Scientific Library）

什么是BNF范式

windows不能在本地计算机上运行oracleDbConsoleorcl

CRC32和CRC8校验代码，C语言版

241 Different Ways to Add Parentheses（C代码版）

Windows下VS开发环境环境安装工程项目设置关于Debug和Release的提示

cs231n斯坦福基于卷积神经网络的CV学习笔记（一）KNN和线性分类器/分类器损失/反向传播一，KNN图像分类算法二，线性分类器三，线性分类器损失四，反向传播五，神经网络

C语言：初学者必定看懂的注释！！！猴子吃桃问题。猴子第一天摘下若干个桃子，每天都吃了前一天剩下的一半零一个，到第10天早上想再吃的时候，就剩下一个桃子. 求第一天共摘多少个桃子。

[转]九大排序算法——C语言实现及详解

while 循环、do- while 循环和 for 循环之间的那点事C语言自学之三种循环比较

Windows下配置Apache的SSL服务

Mac｜Windows系统本地照片自动上传到服务器

结构体：typedef与struct的区别

hdu7108哈希

QT5在windows下调用OpenCV库出现: undefined reference to `xxxxx&amp;#39; 错误解决办法（适用MinGW编译器）。

继续阅读

QT5在windows下调用OpenCV库出现: undefined reference to `xxxxx' 错误解决办法（适用MinGW编译器）。