cmake变量cmake_prefix_path是什么，如何使用

CMake变量cmake_prefix_path是用于设置项目依赖库的搜索路径的。通过设置该变量，可以让CMake在指定的路径中查找依赖库，而不是在默认路径中查找。

使用方法如下：
set(cmake_prefix_path "path/to/dependencies")
在具体的CMake项目中，可以根据实际情况进行设置。

相关问题

message("CMAKE_PREFIX_PATH = ${CMAKE_PREFIX_PATH}") message("CMAKE_MODULE_PATH = ${CMAKE_MODULE_PATH}")是空的

如果输出的`CMAKE_PREFIX_PATH`和`CMAKE_MODULE_PATH`为空，可能是因为在你的CMakeLists.txt文件中没有显式地设置这些变量的值。在这种情况下，CMake将使用默认的查找路径。

默认情况下，CMake会在以下路径中查找库和头文件：

- 系统路径
- CMAKE_PREFIX_PATH环境变量指定的路径
- CMAKE_INSTALL_PREFIX变量指定的路径
- CMAKE_SYSTEM_PREFIX_PATH变量指定的路径
- CMAKE_SYSTEM_LIBRARY_PATH变量指定的路径
- CMAKE_SYSTEM_INCLUDE_PATH变量指定的路径

如果你想自定义查找路径，可以在CMakeLists.txt中设置`CMAKE_PREFIX_PATH`和`CMAKE_MODULE_PATH`变量的值。例如：

set(CMAKE_PREFIX_PATH "/path/to/my/lib;/path/to/other/lib")
set(CMAKE_MODULE_PATH "/path/to/my/cmake/modules;/path/to/other/cmake/modules")

这样就会在指定的路径中查找库和模块文件。

# toplevel CMakeLists.txt for a catkin workspace # catkin/cmake/toplevel.cmake cmake_minimum_required(VERSION 3.0.2) project(Project) set(CATKIN_TOPLEVEL TRUE) # search for catkin within the workspace set(_cmd "catkin_find_pkg" "catkin" "${CMAKE_SOURCE_DIR}") execute_process(COMMAND ${_cmd} RESULT_VARIABLE _res OUTPUT_VARIABLE _out ERROR_VARIABLE _err OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_STRIP_TRAILING_WHITESPACE ) if(NOT _res EQUAL 0 AND NOT _res EQUAL 2) # searching fot catkin resulted in an error string(REPLACE ";" " " _cmd_str "${_cmd}") message(FATAL_ERROR "Search for 'catkin' in workspace failed (${_cmd_str}): ${_err}") endif() # include catkin from workspace or via find_package() if(_res EQUAL 0) set(catkin_EXTRAS_DIR "${CMAKE_SOURCE_DIR}/${_out}/cmake") # include all.cmake without add_subdirectory to let it operate in same scope include(${catkin_EXTRAS_DIR}/all.cmake NO_POLICY_SCOPE) add_subdirectory("${_out}") else() # use either CMAKE_PREFIX_PATH explicitly passed to CMake as a command line argument # or CMAKE_PREFIX_PATH from the environment if(NOT DEFINED CMAKE_PREFIX_PATH) if(NOT "$ENV{CMAKE_PREFIX_PATH}" STREQUAL "") if(NOT WIN32) string(REPLACE ":" ";" CMAKE_PREFIX_PATH $ENV{CMAKE_PREFIX_PATH}) else() set(CMAKE_PREFIX_PATH $ENV{CMAKE_PREFIX_PATH}) endif() endif() endif() # list of catkin workspaces set(catkin_search_path "") foreach(path ${CMAKE_PREFIX_PATH}) if(EXISTS "${path}/.catkin") list(FIND catkin_search_path ${path} _index) if(_index EQUAL -1) list(APPEND catkin_search_path ${path}) endif() endif() endforeach() # search for catkin in all workspaces set(CATKIN_TOPLEVEL_FIND_PACKAGE TRUE) find_package(catkin QUIET NO_POLICY_SCOPE PATHS ${catkin_search_path} NO_DEFAULT_PATH NO_CMAKE_FIND_ROOT_PATH) unset(CATKIN_TOPLEVEL_FIND_PACKAGE) if(NOT catkin_FOUND) message(FATAL_ERROR "find_package(catkin) failed. catkin was neither found in the workspace nor in the CMAKE_PREFIX_PATH. One reason may be that no ROS setup.sh was sourced before.") endif() endif() catkin_workspace()

根据您提供的 CMakeLists.txt 文件，这是一个用于构建 catkin 工作空间的顶层 CMakeLists.txt 文件。该文件负责搜索并包含 catkin 软件包。

首先，它尝试在工作空间内搜索并包含 catkin 软件包。如果成功找到并包含了 catkin 软件包，则会添加子目录并编译该软件包。

如果在工作空间内未找到 catkin 软件包，则会尝试使用 CMAKE_PREFIX_PATH 环境变量或作为命令行参数传递给 CMake 的 CMAKE_PREFIX_PATH 变量来搜索 catkin。它会在 CMAKE_PREFIX_PATH 中搜索所有可能的 catkin 工作空间，并尝试找到 catkin 软件包。

如果仍然无法找到 catkin 软件包，则会输出错误消息。

此外，它还调用了 `catkin_workspace()` 函数，用于标记当前目录为 catkin 工作空间。

请确保您的系统中已经正确安装了 catkin，并且工作空间的目录结构和设置是正确的。如果您遇到任何问题，请提供更多详细信息，我将尽力帮助您解决问题。