注意
本文最后更新于 2024-02-01，文中内容可能已过时。
一、导言
导言
废弃是在不断发展的项目开发过程中一种重要机制，它向开发人员发出信号，表明将来某个函数、宏或变量将被删除或替换。在一段时间内，函数、宏或变量将继续可访问，但会发出警告，最终可能会上升为错误。
二、项目结构
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| .
├── cmake
│ └── custom_guard.cmake
└── CMakeLists.txt
|
项目结构：
https://gitee.com/jiangli01/tutorials/tree/master/cmake-tutorial/chapter7/06
三、相关源码
CMakeLists.txt
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| cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
project(example LANGUAGES NONE)
macro(custom_include_guard)
if(NOT DEFINED included_modules)
set(included_modules)
endif()
if ("${CMAKE_CURRENT_LIST_FILE}" IN_LIST included_modules)
message(WARNING "module ${CMAKE_CURRENT_LIST_FILE} processed more than once")
endif()
list(APPEND included_modules ${CMAKE_CURRENT_LIST_FILE})
endmacro()
function(deprecate_variable _variable _access)
if(_access STREQUAL "READ_ACCESS")
message(DEPRECATION "variable ${_variable} is deprecated")
endif()
endfunction()
if (CMAKE_VERSION VERSION_GREATER "3.9")
# deprecate custom_include_guard
macro(custom_include_guard)
message(DEPRECATION "custom_include_guard is deprecated - use built-in include_guard instead")
_custom_include_guard(${ARGV})
endmacro()
# deprecate variable included_modules
variable_watch(included_modules deprecate_variable)
endif()
include(cmake/custom_guard.cmake)
message(STATUS "list of all included modules: ${included_modules}")
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引用
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| macro(custom_include_guard)
if(NOT DEFINED included_modules)
set(included_modules)
endif()
if ("${CMAKE_CURRENT_LIST_FILE}" IN_LIST included_modules)
message(WARNING "module ${CMAKE_CURRENT_LIST_FILE} processed more than once")
endif()
list(APPEND included_modules ${CMAKE_CURRENT_LIST_FILE})
endmacro()
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定义了一个自定义的包含保护机制，包括一个自定义模块(与上一篇内容相同)，并打印所有包含模块的列表。对于CMake 3.10或更高版本有内置的include_guard。但是，不能简单地删除custom_include_guard和${included_modules}，而是使用一个废弃警告来弃用宏和变量。某个时候，可以将该警告转换为FATAL_ERROR，使代码停止配置，并迫使开发人员对代码进行修改，切换到内置命令。
引用
废弃函数、宏和变量的方法如下:
1.定义一个函数，使用它来弃用一个变量
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| function(deprecate_variable _variable _access)
if(_access STREQUAL "READ_ACCESS")
message(DEPRECATION "variable ${_variable} is deprecated")
endif()
endfunction()
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2.如果CMake的版本大于3.9，我们重新定义custom_include_guard并将variable_watch附加到included_modules中:
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| if (CMAKE_VERSION VERSION_GREATER "3.9")
# deprecate custom_include_guard
macro(custom_include_guard)
message(DEPRECATION "custom_include_guard is deprecated - use built-in include_guard instead")
_custom_include_guard(${ARGV})
endmacro()
# deprecate variable included_modules
variable_watch(included_modules deprecate_variable)
endif()
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cmake/custom_guard.cmake
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| custom_include_guard()
message(STATUS "custom.cmake is included and processed")
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四、结果展示
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| $ mkdir -p build
$ cd build
$ cmake ..
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CMake3.10以下版本的项目会产生以下结果:
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| -- custom_custom.cmake is included and processed
-- list of all included modules: /home/jiangli/repo/tutorials/cmake-tutorial/chapter7/06/cmake/custom.cmake
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CMake3.10以下版本的项目会产生以下结果:
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| CMake Deprecation Warning at CMakeLists.txt:26 (message):
custom_include_guard is deprecated - use built-in include_guard instead
Call Stack (most recent call first):
cmake/custom_guard.cmake:1 (custom_include_guard)
CMakeLists.txt:34 (include)
-- custom_custom.cmake is included and processed
CMake Deprecation Warning at CMakeLists.txt:19 (message):
variable included_modules is deprecated
Call Stack (most recent call first):
CMakeLists.txt:9999 (deprecate_variable)
CMakeLists.txt:36 (message)
-- list of all included modules: /home/jiangli/repo/tutorials/cmake-tutorial/chapter7/06/cmake/custom_guard.cmake
-- Configuring done
-- Generating done
-- Build files have been written to: /home/jiangli/repo/tutorials/cmake-tutorial/chapter7/06/build
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