What is the best way to join a list in CMake into a string?
By joining I mean convert SET(somelist \"a\" \"b\" \"c\\;c\") to \"a:b:c;c\" where the glue string (\":\") i
Usually this task is solved with simple string REPLACE
command. You can find a number of such replaces in scripts coming with cmake. But if you really need to care about semicolons inside you values, then you can use the following code:
function(JOIN VALUES GLUE OUTPUT)
string (REGEX REPLACE "([^\\]|^);" "\\1${GLUE}" _TMP_STR "${VALUES}")
string (REGEX REPLACE "[\\](.)" "\\1" _TMP_STR "${_TMP_STR}") #fixes escaping
set (${OUTPUT} "${_TMP_STR}" PARENT_SCOPE)
endfunction()
SET( letters "" "\;a" b c "d\;d" )
JOIN("${letters}" ":" output)
MESSAGE("${output}") # :;a:b:c:d;d
CMake 3.12 is poised to finally add this upstream:
https://github.com/Kitware/CMake/commit/a58158727be4585f9fd71449e9cc9e801c59a009
https://github.com/Kitware/CMake/commit/689eeb67cb87a9ed1d91a4971806488d00e68f42
You can use the string REPLACE function:
function(JOIN VALUES GLUE OUTPUT)
string (REPLACE ";" "${GLUE}" _TMP_STR "${VALUES}")
set (${OUTPUT} "${_TMP_STR}" PARENT_SCOPE)
endfunction()
#USAGE:
SET(somelist a b c)
JOIN("${somelist}" ":" output)
MESSAGE("${output}") # will output "a:b:c"
The answers above are ok, when you do not use semicolons or when you can (and want to) escape them. I prefer not to escape semicolons, so I wrote the following function:
function(JOIN OUTPUT GLUE)
set(_TMP_RESULT "")
set(_GLUE "") # effective glue is empty at the beginning
foreach(arg ${ARGN})
set(_TMP_RESULT "${_TMP_RESULT}${_GLUE}${arg}")
set(_GLUE "${GLUE}")
endforeach()
set(${OUTPUT} "${_TMP_RESULT}" PARENT_SCOPE)
endfunction()
The advantage is that the list can be empty and it doesn't have to be in a variable (but may be written in the place of invocation).
The usage is:
set(SOME_LIST a b c d)
join(RESULT "/" ${SOME_LIST})
message(STATUS "RESULT='${RESULT}'") # outputs RESULT='a/b/c/d'
# or
join(RESULT " " e f g h)
message(STATUS "RESULT='${RESULT}'") # outputs RESULT='e f g h'