[Rd] readBin(what="character", n=overcount)->extra "" in result (PR#9363)

[bill at insightful.com]

On Mon, 13 Nov 2006 bill at insightful.com wrote:

> When I use readBin() to read an unknown number
> of null-terminated strings from a file by supplying
> an overcount as the n= argument, it appends an empty
> string to the result.
>
> > tf<-tempfile()
> > strings<-c("One","Two","Three")
> > writeBin(strings, con=tf)
> > readBin(con=tf,what="character",n=100) # expect "One","Two","Three" only
> [1] "One"   "Two"   "Three" ""

I think the fix is to src/library/connections.c, where
m (the number of items read) is initialized to 1 instead
of 0.  It is later used to shorten the vector of read
objects:
    if(m < n) {
        PROTECT(ans = lengthgets(ans, m));
        UNPROTECT(1);
    }

*** connections.c-orig	2006-09-13 19:05:06.000000000 -0700
--- connections.c	2006-11-13 11:46:35.000000000 -0800
***************
*** 2740,2746 ****
      if(!strcmp(what, "character")) {
  	SEXP onechar;
  	PROTECT(ans = allocVector(STRSXP, n));
! 	for(i = 0, m = i+1; i < n; i++) {
  	    onechar = isRaw ? rawOneString(bytes, nbytes, &np)
  		: readOneString(con);
  	    if(onechar != R_NilValue) {
--- 2740,2746 ----
      if(!strcmp(what, "character")) {
  	SEXP onechar;
  	PROTECT(ans = allocVector(STRSXP, n));
! 	for(i = 0, m = 0; i < n; i++) {
  	    onechar = isRaw ? rawOneString(bytes, nbytes, &np)
  		: readOneString(con);
  	    if(onechar != R_NilValue) {