[Rd] readBin(what="character", n=overcount)->extra "" in result (PR#9361)

[Prof Brian Ripley]

That's arrived after I had committed an identical fix.  It's a relic of a 
time when m had a different meaning.

Thanks!

Brian

On Mon, 13 Nov 2006, Bill Dunlap wrote:

> 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) {
>
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>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595