“找不到-l <目录>”错误-CMake

错误：

/usr/bin/ld: cannot find -lraspicam/main_folder/opencv-plus/

发生这种情况是因为您尝试在此处将目录链接到frame_cap可执行文件：

TARGET_LINK_LIBRARIES( frame_cap ${OpenCV_LIBS} ${OpenCVPLUS_DIR})

这没有道理；只有库应该链接到您的可执行文件。

从您的评论看来，您好像要构建两个可执行文件，但要同时使用两个grab_cut函数。使用CMake当然可以实现这一点。但是您似乎遇到了设计问题，因为假设两个文件都包含一个函数grab_cut.cpp，则使用frame_cap可执行文件编译文件可能会引起问题main。您需要将函数拆分main为一个单独的文件（例如main.cpp），然后可以将其包含grab_cut.cpp在两个可执行文件的编译中。

顺便说一句，您可以使用它CMAKE_CURRENT_LIST_DIR来引用当前CMakeLists.txt文件的目录，因此无需在源树中明确列出目录。另外，我祈祷您使用的是比2.8版更新的CMake。CMake文件中的某些步骤似乎是不必要的，因此以下是一些可能适合您的简化文件。

CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
PROJECT(frame_cap)

# There is no need to spell out this directory since it exists 
# in the source-tree already.
SET(OpenCVPLUS_DIR "/home/pi/Desktop/raspicam/main_folder/opencv-plus")

FIND_PACKAGE( OpenCV REQUIRED )
# Seems unused, remove it.
SET(OpenCV_PACKAGE ${OpenCV_LIBRARIES})

# Include the OpenCV and opencv-plus headers in this executable.
INCLUDE_DIRECTORIES(${OpenCV_INCLUDE_DIRS} ${CMAKE_CURRENT_LIST_DIR}/opencv-plus)
# There is no library to link from this directory, so we don't need this call.
LINK_DIRECTORIES(${OpenCVPLUS_DIR})

ADD_SUBDIRECTORY(opencv-plus) 

# Add the grap_cut.cpp file to the frame_cap executable.
ADD_EXECUTABLE( frame_cap frame_cap.cpp opencv-plus/grab_cut.cpp)
# We don't link anything from opencv-plus, we compiling it directly.
TARGET_LINK_LIBRARIES( frame_cap ${OpenCV_LIBS} ${OpenCVPLUS_DIR})

您的opencv-plus/CMakeLists.txt文件可以简化为以下形式：

# If this CMake file is always called as part of the top-level CMake 
# file, don't need this.
CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
PROJECT(grab_cut)
# Don't need this, as explained earlier.
SET(OpenCVPLUS_DIR "/home/pi/Desktop/raspicam/main_folder/opencv-plus")
# The top-level CMake file already found OpenCV, so the variables 
# we need are already defined.
FIND_PACKAGE(OpenCV REQUIRED)

# The include directories get initialized from the parent CMake file, so no need 
# for this call if the include directories are the same for both executables.
INCLUDE_DIRECTORIES(${OpenCV_INCLUDE_DIRS})
# Separate 'main' function into separate file, and add it here.
SET(SOURCES grab_cut.cpp grab_cut.h main.cpp)

# Don't need to add 'grab_cut.cpp' to the executable twice! It was 
# already added using the 'SOURCES' variable.
ADD_EXECUTABLE(grab_cut grab_cut.cpp ${SOURCES})
TARGET_LINK_LIBRARIES(grab_cut ${OpenCV_LIBS})