There are a few problems. First, common C standard library implementations also include POSIX implementations, unnecessarily conflating the two. POSIX does not

There are a few problems. First, common C standard library implementations also include POSIX implementations, unnecessarily conflating the two. POSIX does not require `getaddrinfo` to implement DNS over TCP, indeed it doesn't even have to use DNS at all. Second, many programs rely on the OS-provided DNS when using a more capable library would be a better choice. Then they don't read the documentation for `getaddrinfo`, fail to check the `hints` field returned to see that it's UDP only, and still try to fall back to TCP and return an inevitably confusing error. POSIX `getaddrinfo` is usually not what you want, but unfortunately it often works well enough that you don't notice until someone tries to run your program on a different OS.