c++ - 与 raspicam 库链接时链接器/加载器错误 "undefined reference to ..."

Question

我正在尝试使用 cmake 编译一个简单的项目，同时使用 raspicam 库。项目编译完美；但是，最后我有 ld 错误。 Raspicam 从这里下载:http://www.uco.es/investiga/grupos/ava/node/40 .有什么想法吗？

ma​​in.cpp:

#include <raspicam_cv.h>

int main ( int argc,char **argv ) {
    raspicam::RaspiCam_Cv capture;

    if (!capture.open()) {
        return 1;
    }
    return 0;
}

CMakeLists.txt:

cmake_minimum_required(VERSION 3.10)
project(raspicam)

set(CMAKE_CXX_STANDARD 17)
include_directories(raspicam-0.1.6/src)
link_directories(raspicam-0.1.6/src)
add_executable(raspicam main.cpp)
set(RASPICAM_LIB ${CMAKE_SHARED_LIBRARY_PREFIX}raspicam_cv${CMAKE_SHARED_LIBRARY_SUFFIX})
target_link_libraries(raspicam ${RASPICAM_LIB})

构建命令:

cd raspicam-0.1.6/ && cmake -DOpenCV_DIR=/home/user/Projects/opencv/opencv-build . && make && cd .. && cmake . && make

错误:

CMakeFiles/raspicam.dir/main.cpp.o: In function `main':
/home/user/CLionProjects/raspicam/main.cpp:5: undefined reference to `raspicam::RaspiCam_Cv::RaspiCam_Cv()'
/home/user/CLionProjects/raspicam/main.cpp:7: undefined reference to `raspicam::RaspiCam_Cv::open()'
/home/user/CLionProjects/raspicam/main.cpp:5: undefined reference to `raspicam::RaspiCam_Cv::~RaspiCam_Cv()'
/home/user/CLionProjects/raspicam/main.cpp:5: undefined reference to `raspicam::RaspiCam_Cv::~RaspiCam_Cv()'
collect2: error: ld returned 1 exit status
CMakeFiles/raspicam.dir/build.make:94: recipe for target 'raspicam' failed
make[2]: *** [raspicam] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/raspicam.dir/all' failed
make[1]: *** [CMakeFiles/raspicam.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

Answer 1

看来您正在尝试从源代码构建 raspicam。看着 documentation you linked raspicam 似乎提供了一个 CMake 查找包，并鼓励用户像这样包含该库:

project (my_raspi_project)
find_package(raspicam REQUIRED)
add_executable (my_raspi_project main.cpp)  
target_link_libraries (my_raspi_project ${raspicam_LIBS})

我鼓励您这样做，但这需要在您的系统上安装 raspicam。也就是说，您首先需要按照上述文档中列出的安装步骤进行操作:

tar xvzf raspicamxx.tgz
cd raspicamxx
mkdir build
cd build
cmake ..
make
sudo make install
sudo ldconfig

这会将包安装在 CMake 可以找到它的位置，并允许 CMakeList.txt 中使用的 find_package(raspicam REQUIRED) 正常工作。

如果您无法将库安装到您的开发机器上，而是希望在您的项目旁边从源代码构建它，您可以考虑:

1. 使用 CMake 的 add_subdirectory命令

2. 使用 CMake 的 ExternalProject_Add命令。

选项 #1 将允许您将 CMakeList.txt 文件更新为如下所示:

cmake_minimum_required(VERSION 3.10)
project(raspicam)

set(CMAKE_CXX_STANDARD 17)
add_subdirectory(<path to raspicam CMakeList.txt>)
add_executable(my_raspicam_program main.cpp)
target_link_libraries(my_raspicam_program raspicam)

请注意，您需要将目标名称 raspicam 更改为唯一的名称，因为该目标名称由您包含在 add_subdirectory 中的包使用。

选项 #2 更复杂，但有一个额外的好处，即您不会在版本控制系统中跟踪 raspicam 源代码。