Yea, one of the reasons I rolled my own libc equivalent is how actually awful glibc (and the STL) are. If you actually read the glibc source you'll find countless comments such as "TODO: we need to account for X failure state" or ridiculous UB prone codepaths (signal trampolines, TLS, threading for instance). As in, these are things that can and SHOULD be guarded by the libc itself instead they just allow plain UB to occur.

The STL is awful by extension because it delegates ALL of this work to libc (anything that interacts with the OS) and they integrate this deeply into every single container.