Unknown CMake command “list_spaces_append

本文链接：https://blog.youkuaiyun.com/dragoo1/article/details/124398366

这篇博客详细介绍了curl-7.26.0版本中CMake的自定义函数list_spaces_append_once的实现原理和用途。该函数用于将列表元素以空格分隔转换为字符串，并避免重复添加。当在其他curl版本的CMakeLists.txt文件中尝试使用此函数而未定义时，会导致编译错误。

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list_spaces_append_once是curl-7.26版本的一个自定义cmake函数

在curl-7.26.0\CMake\Utilities.cmake文件里

# Converts a CMake list to a string containing elements separated by spaces
function(TO_LIST_SPACES _LIST_NAME OUTPUT_VAR)
  set(NEW_LIST_SPACE)
  foreach(ITEM ${${_LIST_NAME}})
    set(NEW_LIST_SPACE "${NEW_LIST_SPACE} ${ITEM}")
  endforeach()
  string(STRIP ${NEW_LIST_SPACE} NEW_LIST_SPACE)
  set(${OUTPUT_VAR} "${NEW_LIST_SPACE}" PARENT_SCOPE)
endfunction()

# Appends a lis of item to a string which is a space-separated list, if they don't already exist.
function(LIST_SPACES_APPEND_ONCE LIST_NAME)
  string(REPLACE " " ";" _LIST ${${LIST_NAME}})
  list(APPEND _LIST ${ARGN})
  list(REMOVE_DUPLICATES _LIST)
  to_list_spaces(_LIST NEW_LIST_SPACE)
  set(${LIST_NAME} "${NEW_LIST_SPACE}" PARENT_SCOPE)
endfunction()

# Convinience function that does the same as LIST(FIND ...) but with a TRUE/FALSE return value.
# Ex: IN_STR_LIST(MY_LIST "Searched item" WAS_FOUND)
function(IN_STR_LIST LIST_NAME ITEM_SEARCHED RETVAL)
  list(FIND ${LIST_NAME} ${ITEM_SEARCHED} FIND_POS)
  if(${FIND_POS} EQUAL -1)
    set(${RETVAL} FALSE PARENT_SCOPE)
  else()
    set(${RETVAL} TRUE PARENT_SCOPE)
  endif()
endfunction()

如果在其他curl版本的CMakeLists.txt文件使用list_spaces_append_once，且Utilities.cmake没有定义函数，会报这类错误