CMake: Howto modify a variable from inside a function

Question

What is the best practice to modify a caller's variable from inside a CMake-function. Assume

function(MyFunction IN_OUT_NAME)

   ... what to do here ...

   string(APPEND ${IN_OUT_NAME} " and that")

   ... what to do here ...

endfunction()

What needs to be done such that the following code fragment

set(MY_MESSAGE "this")
MyFunction(MY_MESSAGE)
message(${MY_MESSAGE})

delivers

this and that

Not-a-duplicate-remarks:

Modify a variable inside a function is about JavaScript not CMake
Is JavaScript a pass-by-reference or pass-by-value language? is about JavaScript not CMake

set(variable ${varaible} PARENT_SCOPE) ? – KamilCuk Nov 13 '18 at 10:16 — KamilCuk, Nov 13 '18 at 10:16
Well, that sets it. But how can I read it? – Frank-Rene Schäfer Nov 13 '18 at 10:16 — Frank-Rene Schäfer, Nov 13 '18 at 10:16

score 2 · Accepted Answer · answered Nov 13 '18 at 10:18

Just use PARENT_SCOPE to export the value to parent scope.

function(MyFunction IN_OUT_NAME)
   string(APPEND ${IN_OUT_NAME} " and that")
   set(${IN_OUT_NAME} "${${IN_OUT_NAME}}" PARENT_SCOPE)
endfunction()

set(MY_MESSAGE "this")
MyFunction(MY_MESSAGE)
message(${MY_MESSAGE})

CMake: Howto modify a variable from inside a function

1 Answers1