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_use_lfn
========

Syntax
------

     #include <fcntl.h>
     
     char _use_lfn(const char *path);

Description
-----------

The `_use_lfn' function returns a nonzero value if the low level libc
routines will use the "Long File Name" (LFN) functions provided with
Windows 9x (and other advanced filesystems), when accessing files and
directories on the same filesystem as PATH.  PATH may be any legal
pathname; however, the function only needs the name of the root
directory on the particular drive in question.  If PATH is a `NULL'
pointer, the function assumes that all the filesystems support (or do
not support) LFN in the same manner, and returns the info pertinent to
the last filesystem that was queried; this usually makes the call
faster.  Note that on Windows 95 you don't need to distinguish between
different drives: they all support LFN API.  If PATH does not specify
the drive explicitly, the current drive is used.

The header `fcntl.h' defines a macro `_USE_LFN'; applications should
use this macro instead of calling `_use_lfn' directly.  That is so this
routine could be replaced with one which always returns 0 to disable
using long file names.  Calling `_USE_LFN' also makes the code more
portable to other operating systems, where the macro can be redefined
to whatever is appropriate for that environment (e.g., it should be a
constant 1 on Unix systems and constant 0 for environments that don't
support LFN API, like some other MSDOS compilers).  Currently,
`_USE_LFN' assumes that LFN API does *not* depend on a drive.

Long file names can also be disabled by setting the flag
`_CRT0_FLAG_NO_LFN' in `_crt0_startup_flags' for an image which should
not allow use of long file names.  Long names can be suppressed at
runtime on a global basis by setting the environment variable `LFN' to
`N', i.e. `SET LFN=N'.  This might be needed if a distribution expected
the truncation of long file names to 8.3 format to work.  For example,
if a C source routine included the file exception.h (9 letters) and the
file was unzipped as exceptio.h, then GCC would not find the file
unless you set `LFN=n'.  The environment variable can be set in the
`DJGPP.ENV' file to always disable LFN support on any system, or can be
set in the DOS environment for a short term (single project) basis.  If
you dual boot a system between Windows 95 and DOS, you probably should
set `LFN=n' in your `DJGPP.ENV' file, since long file names would not
be visible under DOS, and working with the short names under DOS will
damage the long names when returning to Windows 95.

Return Value
------------

If LFN APIs are supported and should be used, it returns 1, else 0.

Note that if the `_CRT0_FLAG_NO_LFN' bit is set, or `LFN' is set to `N'
or `n' in the environment, both `_use_lfn' and `_USE_LFN' will always
return 0 without querying the filesystem.  You can reset the
`_CRT0_FLAG_NO_LFN' bit at runtime to force filesystem to be queried.

Example
-------


     #include <fcntl.h>
     #include <sys/stat.h>
     
       int fd = creat (_USE_LFN ? "MyCurrentJobFile.Text" : "currjob.txt",
                       S_IRUSR | S_IWUSR);