Version regular expression in CMake

Question

I want to validate user-specified version string - to ensure it consists of three period-separated numbers (e.g. 1.20.300).
But i'm not sure how to write such regex, the code below is just a try:

if( PROJECT_VERSION MATCHES "([0-9]+).([0-9]+).([0-9+])" )
    message( "NOTE: Valid version string" )
else()
    message( FATAL_ERROR "Invalid version string" )
endif()

So, how to correctly write required regex?
Thanks.

UPD
My regex also matches 1.2.3.4, but is should not!
Only three period-separated numbers are possible.

Answer 1

Dots are special in regex, so you should escape them:

"^([0-9]+)\\.([0-9]+)\\.([0-9]+)$"

Why double-backslash? See here: https://stackoverflow.com/a/4490920/4323