NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/14443

Internet Message Format | 1996-08-05 | 1.8 KB

Path: wkaufman.us.oracle.com!wkaufman
From: [e-mail] (William Kaufman)
Newsgroups: comp.lang.c
Subject: Re: Q: "Overlapping Objects"
Date: 14 Apr 1996 23:10:48 GMT
Organization: Oracle Corporation, Redwood Shores CA
Message-ID: <4ks0lo$[e-mail]>
References: <[e-mail]>
NNTP-Posting-Host: wkaufman.us.oracle.com

In article <[e-mail]> Richard Steadman <[e-mail]> writes:
] Hello.
]
] I have a question which is quite simple, but I can't seem to find
] the right answer anywhere.
]
] I'm trying to figure out when it is necessary to use the memmove()
] function when copying strings. K&R and the man page says to use it
] when the "objects overlap". But I can't find a formal definition
] for this phrase (it's not in the FAQ either -- I checked!).

    If you've got two pointers into the same piece of memory, they
overlap if either pointer is in the middle of the other's region (i.e.,
between the other pointer and that pointer plus the size you're
copying).

] Here's the scenario: I have a string, and want to copy the tail of
] it to an earlier part of the string. The two pieces are *not*
] overlappng when the function is called, but they may be when the
] copy is finished.
]
] Given this, it safe to use strcat() instead of memmove()?

    I'm not sure I understand--they either overlap or they don't, and
asking _at what time_ fixed chunks of memory overlap doesn't make sense
to me.  But I think your answer is "No".

                                           -- Bill K.

Bill Kaufman             | "I mean ... it's not even been a two-and-two-make-
[e-mail]   |  five sort of day, it's more like a two-and-two-
                         |  make ... *fish* ..."  -- "Cages", Dave McKean