tmpnam.3s

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3S 代码 · 共 131 行

.\" SCCSID: @(#)tmpnam.3s	8.1	9/11/90
.TH tmpnam 3s 
.SH Name
tmpnam, tempnam \- create a name for a temporary file
.SH Syntax
.B #include <stdio.h>
.PP
.B char \(**tmpnam (s)
.br
.B char \(**s;
.PP
.B char \(**tempnam (dir, pfx)
.br
.B char \(**dir, \(**pfx;
.SH Description
.NXR "tmpnam subroutine"
.NXR "tempnam subroutine"
.NXA "tmpnam subroutine" "tmpfile subroutine"
.NXA "tmpnam subroutine" "mktemp subroutine"
.NXR "temporary file" "naming"
These functions generate file names that can safely be used for
a temporary file.
.PP
The
.PN tmpnam
subroutine
always generates a file name using the path-name defined as
.PN P_tmpdir
in the <stdio.h> header file.
If
.I s\^
is NULL,
.PN tmpnam
leaves its result in an internal static area and returns a pointer
to that area.
The next call to
.PN tmpnam
will destroy the contents of the area.
If
.I s\^
is not NULL,
it is assumed to be the address of an array of at least
.PN L_tmpnam
bytes, where
.PN L_tmpnam
is a constant defined in <stdio.h>;
.PN tmpnam
places its result in that array and returns
.IR s .
.PP
The
.PN tempnam
subroutine allows the user to control the choice of a directory.
The argument
.I dir\^
points to the path-name of the directory in which
the file is to be created.
If
.I dir\^
is NULL or points to a string which is not a path-name
for an appropriate directory, the path-name defined as
.PN P_tmpdir\^
in the <stdio.h> header file is used.
If that path-name is not accessible, 
.PN /tmp
will be used as a last resort.
This entire sequence can be up-staged by
providing an environment variable TMPDIR
in the user's environment, whose value is a path-name for the
desired temporary-file directory.
.PP
Many applications prefer their temporary files to have certain
favorite initial letter sequences in their names.
Use the
.B pfx\^
argument for this.  This argument may be NULL
or point to a string
of up to five characters to be used as the first few characters of the
temporary-file name.
.PP
The
.PN tempnam
subroutine uses 
.MS malloc 3
to get space for the constructed file name,
and returns a pointer to this area.
Thus, any pointer value returned from
.PN tempnam
may serve as an argument to
.I free.
For further information, see 
.MS malloc 3 .
If
.PN tempnam
cannot return the expected result for any reason, that is
.PN malloc
failed, or none of the above mentioned attempts to find
an appropriate directory was successful, a
NULL pointer will be returned.
.NT "Notes"
The
.PN tmpnam
and
.PN tempnam
routines generate a different file
name each time they are called.
.sp
Files created using these functions and either
.PN fopen
or
.PN creat
are temporary only in the sense that they reside in a directory
intended for temporary use, and their names are unique.
It is the user's responsibility to use 
.MS unlink 2
to remove the file when its use is ended.
.NE
.SH Restrictions
If called more than 17,576 times in a single process,
these functions will start recycling previously used names.
.PP
Between the time a file name is created and the file is opened, it
is possible for some other process to create a file with the same name.
This can never happen if that other process is using
these functions or
.PN mktemp ,
and the file names are chosen so as to render duplication by other
means unlikely.
.SH See Also
creat(2), unlink(2), fopen(3s), malloc(3), mktemp(3), tmpfile(3s)