How to do conditional variable assignment with cmake?

Question

I would like to give a default value DEF to a variable VAR if I do not give the flag -DVAR=VAL. Have you any idea?

Thank you.

`if(not VAR) set(VAR "DEF") endif()` ? – KamilCuk Jul 13 '18 at 08:19 — KamilCuk, Jul 13 '18 at 08:19

score 2 · Answer 1 · answered Jul 13 '18 at 11:33

2

The following seems to work. Thanks to Kamil Cuk which leads me to one solution.

if(not defined VAR)
                set(VAR VAL)
 endif()

answered Jul 13 '18 at 11:33

captain_flammy

117
3
9

score 1 · Answer 2 · answered Jul 13 '18 at 20:51

You can just use set(... CACHE ...) command:

set(VAR "DEF" CACHE STRING "My VAR for doing xyz")

If the variable is already set in the cache - e.g. via command line switch -D - it's not overwritten. And the user could change it with cmake-gui or ccmake.

Or if you have boolean values take the option() definitions command.

References

How to do conditional variable assignment with cmake?

2 Answers2