Geany编译器中摄像头初始化报错：undefined reference to raspicam

编译摄像头初始化代码时出现raspicam相关函数未定义引用，导致编译失败。编译命令及报错信息如下：

错误的编译命令 #

g++ $(pkg-config opencv4 --cflags --libs) -o g++ $(pkg-config raspicam --cflags --libs) -o cameratest cameratest.cpp

报错信息 #

/usr/bin/ld: /tmp/cc3JiNr2.o: in function `main':
cameratest.cpp:(.text+0x14): undefined reference to `raspicam::RaspiCam_Cv::RaspiCam_Cv()'
/usr/bin/ld: cameratest.cpp:(.text+0x3c): undefined reference to `raspicam::RaspiCam_Cv::open()'
/usr/bin/ld: cameratest.cpp:(.text+0x9c): undefined reference to `raspicam::RaspiCam_Cv::getId[abi:cxx11]() const'
/usr/bin/ld: cameratest.cpp:(.text+0xd8): undefined reference to `raspicam::RaspiCam_Cv::~RaspiCam_Cv()'
/usr/bin/ld: cameratest.cpp:(.text+0x108): undefined reference to `raspicam::RaspiCam_Cv::~RaspiCam_Cv()'
collect2: error: ld returned 1 exit status
Compilation failed.

问题原因 #

1. 编译命令重复使用-o参数，错误设置输出文件名为g++，导致后续参数逻辑混乱
2. GCC/G++要求源文件在前，链接库参数在后，错误的顺序会让链接器无法匹配raspicam的函数实现

正确的编译命令 #

g++ cameratest.cpp $(pkg-config opencv4 --cflags --libs) $(pkg-config raspicam --cflags --libs) -o cameratest

额外排查步骤 #

如果执行正确命令后仍报错，可检查raspicam库是否安装到位：

pkg-config --modversion raspicam

若返回具体版本号则库安装正常，否则需要重新安装raspicam库。

内容的提问来源于stack exchange，提问作者Talha Faraz