[Rd] [Patch suggestion] Adding 3rd arg to tempfile() to set extension

[Dirk Eddelbuettel]

The other day I was working on an example which used tempfile() to create
file for use by the graphics device. And while I love tempfile()---as it is
portable and clever and the files get cleaned by R and all that---I noticed
one missing feature I would like to see: beside a starting name pattern, and
an optional directory, an 'file extension' argument would be nice to have.
As e.g. in

      tmppdf  <- tempfile(fileext=".pdf")
      tmppng  <- tempfile(fileext=".png")
      tmpjpeg <- tempfile(fileext=".jpeg")

Below is a short and simple patch which extends tempfile() to three arguments
with the new one (fileext) defaulting to "".  If set, the extension is
appended to what we got from R_tmpnam().  I made this non-vectorised; this
could be changed. I left R_tmpnam() alone as its interface appears in a
header. I updated the manual page too.

I wrote this again current R-devel source from SVN, the patch reflects
that. The patch applies cleanly to R-alpha as well where 'make check' passes
(and I only tried this as make check had issues with R-devel but devel being
devel I am not sure that it was this patch).

Now, I understand that tempfile() is used in a large number of places so I
more or less expect to get stone silence or a resounding "don't even think
about it".  This end can always be achieved with a local function; but maybe
somebody else see merit in having this at the source.

Thanks for listening, and for considering this. 

Regards, Dirk

Index: src/library/base/R/temp.R
===================================================================
--- src/library/base/R/temp.R	(revision 54862)
+++ src/library/base/R/temp.R	(working copy)
@@ -14,7 +14,7 @@
 #  A copy of the GNU General Public License is available at
 #  http://www.r-project.org/Licenses/
 
-tempfile <- function(pattern = "file", tmpdir = tempdir())
-    .Internal(tempfile(pattern, tmpdir))
+tempfile <- function(pattern = "file", tmpdir = tempdir(), fileext = "")
+    .Internal(tempfile(pattern, tmpdir, fileext))
 
 tempdir <- function() .Internal(tempdir())
Index: src/library/base/man/tempfile.Rd
===================================================================
--- src/library/base/man/tempfile.Rd	(revision 54862)
+++ src/library/base/man/tempfile.Rd	(working copy)
@@ -12,13 +12,14 @@
   names for temporary files.
 }
 \usage{
-tempfile(pattern = "file", tmpdir = tempdir())
+tempfile(pattern = "file", tmpdir = tempdir(), fileext = "")
 tempdir()
 }
 \arguments{
   \item{pattern}{a non-empty character vector giving the initial part
     of the name.}
   \item{tmpdir}{a non-empty character vector giving the directory name}
+  \item{fileext}{an optional character object giving a file extension}
 }
 \value{
   For \code{tempfile} a character vector giving the names of possible
@@ -55,6 +56,11 @@
   contains a space in any of the components, the path returned will use
   the shortnames version of the path.
 #endif
+
+  The optional argument \code{fileext} can be use to supply a file
+  extension. This can be useful if the temporary file is for example use
+  with a graphics device as the file type can be signalled via the
+  extension; an example would be \code{fileext=".png"}.
 }
 \references{
   Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
Index: src/main/names.c
===================================================================
--- src/main/names.c	(revision 54862)
+++ src/main/names.c	(working copy)
@@ -786,7 +786,7 @@
 {"file.info",	do_fileinfo,	0,	11,	1,	{PP_FUNCALL, PREC_FN,	0}},
 {"file.access",	do_fileaccess,	0,	11,	2,	{PP_FUNCALL, PREC_FN,	0}},
 {"dir.create",	do_dircreate,	0,	11,	4,	{PP_FUNCALL, PREC_FN,	0}},
-{"tempfile",	do_tempfile,	0,	11,	2,	{PP_FUNCALL, PREC_FN,	0}},
+{"tempfile",	do_tempfile,	0,	11,	3,	{PP_FUNCALL, PREC_FN,	0}},
 {"tempdir",	do_tempdir,	0,	11,	0,	{PP_FUNCALL, PREC_FN,	0}},
 {"R.home",	do_Rhome,	0,	11,	0,	{PP_FUNCALL, PREC_FN,	0}},
 {"date",	do_date,	0,	11,	0,	{PP_FUNCALL, PREC_FN,	0}},
Index: src/main/sysutils.c
===================================================================
--- src/main/sysutils.c	(revision 54862)
+++ src/main/sysutils.c	(working copy)
@@ -233,30 +233,44 @@
 
 SEXP attribute_hidden do_tempfile(SEXP call, SEXP op, SEXP args, SEXP env)
 {
-    SEXP  ans, pattern, tempdir;
-    const char *tn, *td;
+    SEXP  ans, pattern, fileext, tempdir;
+    const char *tn, *td, *te;
     char *tm;
-    int i, n1, n2, slen;
+    int i, n1, n2, n3, slen;
+    char tmp1[PATH_MAX];
 
     checkArity(op, args);
-    pattern = CAR(args); n1 = length(pattern);
-    tempdir = CADR(args); n2 = length(tempdir);
+    pattern = CAR(args); n1 = length(pattern); args = CDR(args);
+    tempdir = CAR(args); n2 = length(tempdir); args = CDR(args);
+    fileext = CAR(args); n3 = length(fileext);
     if (!isString(pattern))
 	error(_("invalid filename pattern"));
     if (!isString(tempdir))
 	error(_("invalid '%s' value"), "tempdir");
+    if (!isString(fileext))
+	error(_("invalid pattern for end-of-filename"));
     if (n1 < 1)
 	error(_("no 'pattern'"));
     if (n2 < 1)
 	error(_("no 'tempdir'"));
+    /* fileext is optional and defaults to "" so no test for vector*/
+    if (n3 != 1)
+	error(_("only single argument for end-of-filename pattern supported"));
     slen = (n1 > n2) ? n1 : n2;
     PROTECT(ans = allocVector(STRSXP, slen));
     for(i = 0; i < slen; i++) {
 	tn = translateChar( STRING_ELT( pattern , i%n1 ) );
 	td = translateChar( STRING_ELT( tempdir , i%n2 ) );
+	te = translateChar( STRING_ELT( fileext , 0 ) );
 	/* try to get a new file name */
 	tm = R_tmpnam(tn, td);
-	SET_STRING_ELT(ans, i, mkChar(tm));
+	if (0 != strlen(te)) {
+	   /* append optional extension, or null string */
+	   snprintf(tmp1, PATH_MAX, "%s%s", tm, te);
+	   SET_STRING_ELT(ans, i, mkChar(tmp1));
+	} else {
+	   SET_STRING_ELT(ans, i, mkChar(tm));
+	}
 	if(tm) free(tm);
     }
     UNPROTECT(1);

-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com