Yes, but reordering the headers is usually safe. Having order-dependent behavior is a serious bug and should generally be fixed by the header authors. When you

Yes, but reordering the headers is usually safe. Having order-dependent behavior is a serious bug and should generally be fixed by the header authors. When you add a header do you usually carefully consider the interaction between the new header and all the exist ones? No, you just add it to the end of the existing list or at its sorted position? Yeah, me too. I agree that a formatting tool changing the behavior or performance is a serious issue, but I don't think it's a bug in clang-format in that I suspect it is deliberate design choice, and users can opt out if they want. Maybe the default could be changed or more visible warnings added to the documentation, but the real fix here needs to be in glibc.