What does "whether synchronized I/O can be used with the associated file" mean? From _Advanced Programming in the UNIX® Environment_ : > For `_PC_ASYNC_IO`, `_PC_PRIO_IO`, and `_PC_SYNC_IO`, the referenced file must not be a directory. Name of option | Indicates ... |name argument _POSIX_SYNC_IO |whether synchronized I/O can be used with |_PC_SYNC_IO the associated file So I assume the usage would be `long return_value = pathconf("/a/path/filename",_PC_SYNC_IO)`. It looks like it's a way to get a specific file's "setting". Is this thing can be set to a file? How can I set it? And what does _synchronized I/O_ mean as to a file? I mean, I don't understand how _synchronized I/O_ could be a setting of a file? Shouldn't it be a programming aspect thing instead of merely a "setting"?

The result of `pathconf` can vary depending on the file, for some of the arguments it can be given (`_PC_NAME_MAX`, `_PC_ASYNC_IO`, and a few others), but for most arguments the result is a platform-dependent constant. The values you retrieve using `pathconf` aren’t per-file settings, they’re properties of the system and the type of file; you can’t set them.

Synchronized I/O in this context refers to synchronous reads and writes from and to a file, as controlled by `O_SYNC` and related flags which can be specified on `open` calls. `pathconf(..., _PC_SYNC_IO)` will tell you whether those flags are supported (note that `O_SYNC` is always supposed to be supported on regular files anyway, regardless of the result of `pathconf`).