How to share variables between different CMake fil

Question

How do I share variables between different CMake files, and I show the following examples to illustrate my question:

Main

cmake_minimum_required(VERSION 2.6)
project(test)
set(Var3 "Global variable")

add_subdirectory(${test_SOURCE_DIR}/exe)
add_subdirectory(${test_SOURCE_DIR}/dll)

EXE file

set(Var1 "this is variable 1")
set(Var1 ${Var1} " added to varible 1")
message(STATUS ${Var1})

DLL file

set(Var2 "this is variable 2")
message(STATUS ${Var2})
message(STATUS ${Var1})
message(STATUS ${Var3})

In this example, Var3 can be seen in the CMake files of exe and dll as it is defined in Main. However, Var1, which is defined in exe, will not be observed in dll. I was just curious: is there a way to make Var1 defined in exe observable in dll?

Answer 1

Beside what Tadeusz correctly said, you can make a variable visible at any level (not just one up!) by using

set(Var1 "This is variable 1" CACHE INTERNAL "")

The variable will be available for all the CMake instructions that follow that instruction, so for example it won't be available for a sister directory that is added before the directory where this variable is defined.

Answer 2

The scopes of variable visibility form a tree. The CMakeFiles.txt files added with add_subdirectory have access to the variables defined in themselves, and in the parent scope (the toplevel global scope in your example).

You can export a variable one level up using:

set(Var1 "This is variable 1" PARENT_SCOPE)