@node lock64, io
@findex lock64
@subheading Syntax

@example
#include <io.h>

int lock64(int fd, long long offset, long long length);
@end example

@subheading Description
Locks a region in file @var{fd} using MS-DOS file sharing interface.
The region of @var{length} bytes, starting from @var{offset}, will
become entirely inaccessible to other processes.  If multiple locks are
used on a single file they must be non-overlapping.  The lock must be
removed before the file is closed.

This function will fail unless SHARE, or a network software providing
similar interface, is installed.

Arguments @var{offset} and @var{length} must be of type @code{long
long}, thus enabling you to lock with offsets and lengths as large as
~@math{2^63} (FAT16 limits this to ~@math{2^31}; FAT32 limits this to
@math{2^32-2}).

@xref{unlock64}.

@subheading Return Value
Zero if successful, nonzero if not.


@subheading Portability

@portability !ansi, !posix