最近用Qt写一个项目时出现了undefined reference to 'vtable for class::methode'的错误！
一 描述
程序结构如下：
共享库： libyqmath.so 有个类CMyDraw －－完成一些绘画操作
1. 编译成功，存放在../../../lib/中，即../../../lib/中有libyqmath.so libyqmath.so.1 ...
GUI应用程序：demo
1. 调用CMyDraw进行绘画
2. 在.pro文件中加入了: LIBS += -L../../../li/libyqmath.so
INCLUDEPATH += . ./../../../include ./../../../lib
make时出现如下错误信息：
g++ -Wl,-O1 -o ../../../bin/demo build/cmydrawdlg.o build/cmymathdlg.o build/main.o build/moc_cmydrawdlg.o build/moc_cmymathdlg.o -L/usr/lib -L../../../bin/libyqmath.so -lQtGui -lQtCore -lpthread
build/cmydrawdlg.o: In function `CMyDrawDlg::CMyDrawDlg()':
/home/yangjingtu/projects/study/qt/code/demo/src/cmydrawdlg.cpp:35: undefined reference to `CMyDraw::CMyDraw()'
build/cmydrawdlg.o: In function `~CMyDraw':
/home/yangjingtu/projects/study/qt/code/demo/src/../../yqmath/src/cmydraw.h:36: undefined reference to `vtable for CMyDraw
/home/yangjingtu/projects/study/qt/code/demo/src/../../yqmath/src/cmydraw.h:36: undefined reference to `vtable for CMyDraw
build/cmydrawdlg.o: In function `CMyDrawDlg::MyDraw()':
/home/yangjingtu/projects/study/qt/code/demo/src/cmydrawdlg.cpp:70: undefined reference to `CMyDraw::DrawMyRect(QPicture*, int, int, int, int)'
build/main.o: In function `~CMyDraw':
/home/yangjingtu/projects/study/qt/code/demo/src/../../yqmath/src/cmydraw.h:36: undefined reference to `vtable for CMyDraw
/home/yangjingtu/projects/study/qt/code/demo/src/../../yqmath/src/cmydraw.h:36: undefined reference to `vtable for CMyDraw'
/home/yangjingtu/projects/study/qt/code/demo/src/../../yqmath/src/cmydraw.h:36: undefined reference to `vtable for CMyDraw'
/home/yangjingtu/projects/study/qt/code/demo/src/../../yqmath/src/cmydraw.h:36: undefined reference to `vtable for CMyDraw'
build/cmymathdlg.o: In function `CMyMathDlg::intadd()':
/home/yangjingtu/projects/study/qt/code/demo/src/cmymathdlg.cpp:54: undefined reference to `MyMathInt::add(int, int)'
collect2: 错误：ld 返回 1
二 原因
百度，google了一大圈基本分为两大类：
1. 用了Q_OBJECT的宏，但没有包含其moc文件或没有加到链接列表中去。
2. 所依赖的库文件问题。
排除1，因为共享库已生成成功，那原因就是库或其路径问题。
三 解决方案
尝试1： 更改.pro文件
LIBS += -lyqmath
qmake make后出现： /usr/bin/ld: cannot find -lyqmath
改回
LIBS += -L../../../lin/libyqmath.so
不会出现cannot find问题，那说明路径是对的，程序也找到相应该的库
尝试2： 在/etc/ld.so.conf.d/下添加my-project.conf文件并把路径加进去
sudo vim /ect/ld.so.conf.d/my-project.conf
> .../project/study/qt/lib
sudo ldcofig
再尝试1的方法，问题依旧
尝试3： 更改.pro文件
LIBS += -L../../../lib -lyqmath
qmake make后：太帅了成功了！
一定要注意LIBS的写法！！！！
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