Path: utzoo!utgpu!water!watmath!clyde!bellcore!faline!sabre!gamma!pyuxp!pyuxe!pyuxf!robf2
From: robf2@pyuxf.UUCP (robert fair)
Newsgroups: comp.sys.ibm.pc
Subject: Re: bug in Turbo C 1.5
Summary: Its ANSI s[draft] standard...
Message-ID: <247@pyuxf.UUCP>
Date: 26 Jan 88 20:15:24 GMT
References: <5298@cit-vax.Caltech.Edu>
Organization: Bell Communications Research
Lines: 53

In article <5298@cit-vax.Caltech.Edu>, tim@cit-vax.UUCP writes:
# To the best of my recollection, I don't recall having seen any bug
# reports so far for Turbo C 1.5.  Am I the first person to report a
# bug in Turbo C 1.5?
# 
# This program
# 
# 	----------------------------------
# 	#include <string.h>
# 
# 	void main() {
# 	  char *s = "this is a test";
# 	  printf("%s\n", s);
# 	  memcpy(s + 1, s, strlen(s) - 1);
# 	  printf("%s\n", s);
# 	}
# 	----------------------------------
# 
# displays
# 
# 	--------------
# 	this is a test
# 	tthis is a tes
# 	--------------
# 
# under Turbo C 1.0, and
# 
# 	--------------
# 	this is a test
# 	tthhssii    ee
# 	--------------
# 
# under Turbo C 1.5.
This is precisely correct behaviour - the action of memcpy() on overlapping
regions is undefined in the draft ANSI standard. It looks like Borland took
advantage of this to do memcpy() faster, but it only works on non-overlapping 
areas.

Simply don't use memcpy() on overlapping regions. There should be a function
which does what you want if Turbo is a decent compiler.

Incidently MSC memcpy() changed in *exactly* the same way from 4.0 to 5.0 -
but at leat Microsoft documented the change and provided a function which 
worked in the old way for compatibility [ memmove() ]

Personally I think the entire thing sucks - the function should be
able to detect overlapping areas and take special action in such cases :(
-
-- 
Robert L. Fair
Bell Communications Research/CHC
Piscataway, NJ
{ihnp4,allegra}!pyuxww!pyuxf!robf2