cmake - How to clear/delete a cache variable

Question

Trying to get find_path to do what I want.

find_path(temmp include/help.h)
message("temmp= ${temmp}")

help.h is found. The output is temmp= /usr/local/toolA

find_path(temmp include/foo.shoe)
message("temmp= ${temmp}")

foo.shoe does not exist (not found). The output is temmp= /usr/local/toolA The cache variable exists, so the variable (temmp) is untouched.

I try and clear the cache var with this:

set (temmp "" CACHE INTERNAL "")
find_path(temmp include/help.h)
message("temmp= ${temmp}")

No change. The variable is cleared, but still exists. The output is temmp= (find_path does not run.)

How can I delete the temmp variable from the cache? (I want to force the find_path to run again.)

Answer 1

You can use unset:

unset(temmp CACHE)

As an aside, the find_path calls should be more like:

find_path(temmp help.h include)