While writing my code I thought of having a common implementation for all POSIX OSes as opposed to separate implementation for each OS. One of the POSIX API I use is posix_fallocate() and while testing I found it not being supported by MacOS.
Had I known this earlier I would have not used this API or have had separate implementations for each OS.
So my question is - what is an easy way to find support for a particular posix call in different OSes? Do people always have to search documentation for each target OS?
Thanks.
Looking at the documentation is a good start, but it often won't tell you when a particular function has been implemented, which is also important. For obscure platforms, it may be difficult to tell which older versions are still relevant, which makes it even harder to decide whether a dependency on a particular POSIX feature is acceptable.
The other question is whether a feature is implemented, but with substandard quality. posix_fallocate is an interesting corner case in this regard. The glibc implementation uses emulation if the file system lacks support for an actual low-level fallocate operation (such as NFS until recently):
Depending on what your application does, this behavior might not be acceptable. Just checking header files and documentation might not reveal this (the Note part in the documentation above was added only recently, for example).
In the end, there isn't a good substitute for building and testing as early as possible on all relevant targets, but I understand that this is increasingly difficult for non-Linux targets.