NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/14565

Internet Message Format | 1996-08-05 | 1.6 KB

Path: news.ov.com!news
From: [e-mail] ([e-mail])
Newsgroups: comp.lang.c
Subject: Re: char* still alive after free ???
Date: 15 Apr 1996 20:24:04 GMT
Organization: OpenVision
Message-ID: <4kub94$[e-mail]>
References: <[e-mail]>
Reply-To: [e-mail]
NNTP-Posting-Host: foghorn.pls.ov.com

In article [e-mail], Markus Heller <[e-mail]> writes:
>Hi,
>
>I have a global variable :
>
>char *text=NULL;
>
>I want to use it to store different "strings" (at diffreent times).
>E.g., if I want to sore 10 characters in text, I do a
>text=(char *) malloc(10*sizeof(char));
>When I want to use text to store 3 other characters, I first do a
>free(text); text=NULL; and finally a
>text=(char *) malloc(3*sizeof(char));
>But to my surprise there are still the 4thh to 10th charcter of
>text contained before the free(text)/malloc... ???
>This happens under linux, but why ?
>(what I want to to is to get filenames from the user and then open those
> files by a function to which I pass the file name..)
>
>Markus


1.  There is no requirement for the memory allocated by malloc() to
    be initialized.  The user is responsible for initialization.

2.  malloc() may re-use memory made available by free().

3.  You were violating the terms of malloc by looking past the
    third char.  You could have caused some form of memory protection
    error.  BTW, if you were going to store strings, don't forget
    to make room for the trailing null character in your memory allocation
    requests.

            [e-mail]