Definitely recommend using -isystem for third party libs such as Boost, ACE, QT, Protobuf, etc. I strive for warning free code in my own, but dont have much control over the libs I use. Warnings from Protobuf are especially annoying due to Googles ill-thought-out disregard for signed/unsigned comparison (and their bullshit rationale in their style guideline) and continued use of NULL/0 as a nullptr constant (they only support C++11 and greater, no reason to not use nullptr now). I strive for clean compilation with "-Wall -Wextra -Wzero-as-null-pointer-constant -Werror", but alas, hard to implement after the fact in legacy code.