telldir - return current location in directory stream
The telldir() function returns the current location associated with the directory stream
On success, the telldir() function returns the current location in the directory stream. On error, -1 is returned, and
errno is set appropriately.
Invalid directory stream descriptor
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
In glibc up to version 2.1.1, the return type of telldir() was
off_t. POSIX.1-2001 specifies
long, and this is the type used since glibc 2.1.2.
In early filesystems, the value returned by telldir() was a simple file offset within a directory. Modern filesystems use tree or hash structures, rather than flat tables, to represent directories. On such filesystems, the value returned by telldir() (and used internally by readdir(3)) is a "cookie" that is used by the implementation to derive a position within a directory. Application programs should treat this strictly as an opaque value, making
no assumptions about its contents.
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