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libc.a reference
_use_lfn
Syntax
| | #include <fcntl.h>
char _use_lfn(const char *path);
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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.
Portability
Example
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#include <fcntl.h>
#include <sys/stat.h>
int fd = creat (_USE_LFN ? "MyCurrentJobFile.Text" : "currjob.txt",
S_IRUSR | S_IWUSR);
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