Return a list from the function using OUT parameter

Question

I would like to create a CMake function as:

function(test src_list dst_list)
# do something
endfunction()

usage:

test(${my_lis         


        

Answer 1

In CMake, functions have their own scope, and by default, all modification of variables are local, unless you pass CACHE or PARENT_SCOPE as parameter to set. Inside a function, if you want to modify a variable in the scope of the caller, you should use:

set(${dst_list} <something> PARENT_SCOPE)

See documentation:

A function opens a new scope: see set(var PARENT_SCOPE) for details.

Answer 2

Check that inside your function you are set()ing not dst_list but ${dst_list}. You need this to return data to the parent scope.

Answer 3

Here's how I solved a similar problem which was marked a duplicate of this question. This function takes a string BinaryName and adds it to the list OutVariable which is available in the parent scope. If the list is not defined it is created. I use this strategy for creating new test targets and adding the name of these targets to a list of targets in the main scope.

Thanks to @Tsyvarev for the comments that lead me to figure this out.

function(AddToListFromFunction BinaryName OutVariable)
    if ("${${OutVariable}}" STREQUAL "")
        message(STATUS "1")
        set(${OutVariable} ${BinaryName} PARENT_SCOPE)
        message(STATUS "OutVariable: ${OutVariable} ${${OutVariable}}")
    else ()
        message(STATUS "2")
        set(${OutVariable} "${${OutVariable}}" "${BinaryName}" PARENT_SCOPE)
    endif ()
endfunction()
AddToListFromFunction(MyBinary1 MyTests)
AddToListFromFunction(MyBinary2 MyTests)
message(STATUS "MyTests Variable:  ${MyTests}")