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Date: Tue, 12 Apr 2016 15:07:22 +1000
From: Tony Cook <tony AT develop-help DOT com>
To: cygwin AT cygwin DOT com
Subject: strxfrm() returns an incorrect value on a short buffer
Message-ID: <20160412050722.GE12445@mars.tony.develop-help.com>
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User-Agent: Mutt/1.5.23 (2014-03-12)

strxfrm() returns an incorrect value if you supply an output buffer
and that buffer is too short for the result.

With the code following:

#include <string.h>
#include <locale.h>
#include <stdio.h>

int main() {
  char xbuf[5] = "";
  char *lc = setlocale(LC_ALL, "en_AU.utf8");
  if (!lc) {
    perror("setlocale");
    return 1;
  }
  size_t sza = strxfrm(xbuf, "alphabet", sizeof(xbuf));
  printf("sz: %zd\n", sza);
  size_t szb = strxfrm(NULL, "alphabet", 0);
  printf("sz: %zd\n", szb);

  return 0;
}

On cygwin:

tony AT phobos ~
$ gcc -ostrxfrmtest strxfrmtest.c

tony AT phobos ~
$ ./strxfrmtest
sz: 5
sz: 20

tony AT phobos ~
$ uname -a
CYGWIN_NT-6.1-WOW phobos 2.5.0(0.297/5/3) 2016-04-11 09:55 i686 Cygwin

On Linux:

tony AT mars:~$ gcc -ostrxfrmtest strxfrmtest.c 
tony AT mars:~$ ./strxfrmtest
sz: 26
sz: 26
tony AT mars:~$ uname -a
Linux mars 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt20-1+deb8u3 (2016-01-17) x86_64 GNU/Linux

From looking at the source:

https://cygwin.com/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/nlsfuncs.cc;h=9dbd9b16d53094c60aa835756c967c054ced8e62;hb=HEAD#l1286

It appears that strxfrm() is just returning the size of the output
buffer on an overflow error rather than calling LCMapString() again
with cchDest set to zero to get the required buffer length that
strxfrm() is meant to return on a short buffer.

This came out of the discussion in:

https://rt.perl.org/Ticket/Display.html?id=121734

(not that I've reproduced that issue.)

Tony

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