Global path of the currently open file in xcode 8 project in Swift 3.0

What do you mean by "the currently open file", are you referring to an NSDocument or similar?

For the more general question on how to get the path of an open file, given the filehandle, the following code fetches that information, but it is in C, and I could not find an easy way to call it in Swift, but it is trivial to make a wrapper in Objective-C that returns an NSString:

int ret;
struct vnode_fdinfowithpath vnode_info;
ret = proc_pidfdinfo(getpid(), fd, PROC_PIDFDVNODEPATHINFO, &vnode_info, sizeof(vnode_info));
if (ret < sizeof(vnode_info)) {
    fprintf(stderr, "failed\n");
    return;
}
vnode_info.pvip.vip_path[sizeof(vnode_info.pvip.vip_path) - 1] = '\0';
fprintf(stderr, "%s\n", vnode_info.pvip.vip_path);

For the more general question on how to get the path of an open file, given the filehandle, the following code fetches that information …

That code will work but it relies on libproc which is not public API on iOS-based platforms. A better option is

fcntl

F_GETPATH

import Darwin

func path(for descriptor: Int32) -> String? {
    var path = [CChar](repeating: 0, count: Int(MAXPATHLEN))
    let err = fcntl(descriptor, F_GETPATH, &path)
    guard err == 0 else {
        return nil
    }
    return String(validatingUTF8: path)
}

print(path(for: STDIN_FILENO))
// prints `Optional("/dev/ttys002")` when run from Xcode

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