CMake/Tutorials/SettingVariableGroups

<source lang="cmake"> cmake_minimum_required(VERSION 2.6)

1. The idea of this demo is to show how to set a group of CMake variables together.
2. A common use case is to allow easy enabling/disabling of a large set of targets, while
3. maintaining manual individual target control. This is in contrast to a BUILD_ALL style variable,
4. where targets are build if a corresponding variable to the target is set, OR the BUILD_ALL variable
5. is set. The problem with this method is that if you want to set "all but one" of the targets to ON,
6. it is not possible without manually setting all N-1 of the targets to OFF.

PROJECT(VariablePrefix)

1. Add options to build specific targets

option(build_Green "Green doc string.") option(build_Blue "Blue doc string.")

1. Add options to allow enabling/disabling of a set of targets

option(TurnOnAll "Turn on all build_ variables.") option(TurnOffAll "Turn off all build_ variables.")

1. A function to get all user defined variables with a specified prefix

function (getListOfVarsStartingWith _prefix _varResult)

   get_cmake_property(_vars CACHE_VARIABLES)
   string (REGEX MATCHALL "(^|;)${_prefix}[A-Za-z0-9_]*" _matchedVars "${_vars}")
   set (${_varResult} ${_matchedVars} PARENT_SCOPE)

endfunction()

1. Mass toggle "commands". These variables (TurnOnAll and TurnOffAll) let you
2. enable or disable all of the variables starting with "build_". This is an abuse
3. of a CMake "variable" to be used as an instruction to issue a command once.
4. For example, when TurnOnAll is set to ON and then configure is run, the following
5. block is run once, and then TurnOnAll sets itself back to OFF.

if(TurnOnAll)

   getListOfVarsStartingWith("build_" matchedVars)
   foreach (_var IN LISTS matchedVars)
       #message("Turn on ${item}")
       get_property(currentHelpString CACHE "${_var}" PROPERTY HELPSTRING)
       set(${_var} ON CACHE BOOL ${currentHelpString} FORCE)
   endforeach()

   get_property(turnOnHelpString CACHE "TurnOnAll" PROPERTY HELPSTRING)
   set(TurnOnAll OFF CACHE BOOL ${turnOnHelpString} FORCE)  # Set itself back to off, as this is a one time thing.

endif()

1. In exactly the same manner, if TurnOffAll is set to ON, all of the variables starting with build_ are set to OFF.

if(TurnOffAll)

   getListOfVarsStartingWith("build_" matchedVars)
   foreach (_var IN LISTS matchedVars)
       #message("Turn off ${item}")
       get_property(currentHelpString CACHE "${_var}" PROPERTY HELPSTRING)
       set(${_var} OFF CACHE BOOL ${currentHelpString} FORCE)
   endforeach()

   get_property(turnOffHelpString CACHE "TurnOffAll" PROPERTY HELPSTRING)
   set(TurnOffAll OFF CACHE BOOL ${turnOffHelpString} FORCE)  # Set itself back to off, as this is a one time thing.

endif()

1. Of course turning on all variables at the same time as turning off all variables does not make sense.

if(TurnOnAllTargets AND TurnOffAllTargets)

 message(FATAL_ERROR "You cannot turn targets on and off at the same time!")

endif()

1. Conditional executables

if(build_Green)

  ADD_EXECUTABLE(Green GroupVariables.cpp)

endif()

if(build_Blue)

  ADD_EXECUTABLE(Blue GroupVariables.cpp)
  # other options here

endif()

</source>

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