打开qt-ros项目时报错：find_package(catkin) failed. catkin was neither found in the workspace···

在打开qt-ros项目时报错：

find_package(catkin) failed. catkin was neither found in the workspace....

原因：

是没有从变量${CMAKE_PREFIX_PATH}中的路径搜索到.catkin

执行 echo ${CMAKE_PREFIX_PATH} 命令发现可以打印出ros路径/opt/ros/melodic。但是CMakeLists.txt指向的/opt/ros/melodic/share/catkin/cmake/toplevel.cmake打印变量${CMAKE_PREFIX_PATH}，发现输出是空的。导致cmake按照cmakelist构建时找不到${CMAKE_PREFIX_PATH}。

解决办法：

 直接修改系统文件

1、打开toplevel.cmake文件

$ sudo gedit /opt/ros/melodic/share/catkin/cmake/toplevel.cmake

2、在文件/opt/ros/melodic/share/catkin/cmake/toplevel.cmake中加入

list(APPEND CMAKE_PREFIX_PATH "/opt/ros/melodic")

修改后的文件如下：

# toplevel CMakeLists.txt for a catkin workspace
# catkin/cmake/toplevel.cmake

cmake_minimum_required(VERSION 3.0.2)

project(Project)

set(CATKIN_TOPLEVEL TRUE)

#add
list(APPEND CMAKE_PREFIX_PATH "/opt/ros/melodic")

# 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()

再次cmake构建qt-ROS的项目，显示成功。

 参考链接：vscode下find_package(catkin) failed错误一种解决方法_/src/cmakelists.txt:65: error: find_package(catkin_王牧犊的博客-CSDN博客