未定义的符号引用，但库已链接

Posted 2023-02-22

【中文标题】未定义的符号引用，但库已链接

【英文标题】：Undefined reference to symbol but library is linked

【发布时间】：2015-10-08 15:38:47

【问题描述】：

我正在尝试使用 opencv 3.0 构建应用程序，但出现“未定义的符号引用错误”

我的问题是符号是在我链接到的库中定义的。

编译命令：

g++ -o DisparityMap main.o tools.o emb.o moc_tools.o moc_emb.o -lopencv_highgui -lopencv_core -lopencv_imgproc -lopencv_imgcodecs -lopencv_calib3d -lQtGui -lQtCore -lpthread

我得到的错误：

/usr/bin/ld: twowindow.o: undefined reference to symbol '_ZN2cv6String10deallocateEv'
//usr/local/lib/libopencv_core.so.3.0: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

但有问题的符号实际上是在我链接到的库中定义的：

scanelf -l -s _ZN2cv6String10deallocateEv | grep _ZN2cv6String10deallocateEv

ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_objdetect.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_photo.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_core.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_video.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_features2d.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_ml.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_highgui.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_videoio.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_stitching.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_videostab.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_superres.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_flann.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_imgproc.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_imgcodecs.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_calib3d.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_shape.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_objdetect.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_photo.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_core.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_video.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_features2d.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_ml.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_highgui.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_videoio.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_stitching.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_videostab.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_superres.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_flann.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_imgproc.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_imgcodecs.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_calib3d.so.3.0.0 
ET_DYN _ZN2cv6String10deallocateEv /usr/local/lib/libopencv_shape.so.3.0.0 

【问题讨论】：

OpenCV 和 Qt 使用相同的编译器构建？

另外，请确保您的库在链接行中的顺序正确。一个库只能依赖于命令行中紧随其后的库。

【参考方案1】：

编译命令：

这不是一个编译命令，它是一个链接命令。

我得到的错误：

错误是引用twowindow.o，这在您的链接命令中不是。

因此，很难相信错误真的来自您提供的链接命令。

很可能，错误来自一个不同的链接命令，而那个链接命令上没有-lopencv_core。

【参考方案2】：

在链接库之前，请给出带有 -L 标志的库的路径。