Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!cbmvax!kevin
From: kevin@cbmvax.UUCP (Kevin Klop)
Newsgroups: comp.sys.amiga
Subject: Re:  Struggling through the "C"
Message-ID: <6597@cbmvax.UUCP>
Date: 12 Apr 89 20:38:39 GMT
References: <2570@ssc-vax.UUCP> <231@nlgvax.UUCP> <6542@cbmvax.UUCP> <17491@cisunx.UUCP>
Reply-To: kevin@cbmvax.UUCP (Kevin Klop)
Organization: Commodore Technology, West Chester, PA
Lines: 83

In article <17491@cisunx.UUCP> ejkst@unix.cis.pittsburgh.edu (Eric J. Kennedy) writes:
>It has been my understanding that "char *a;" gives you a pointer,
>(pointing to some arbitrary place), while "char a[80];" actually
>allocates 80 bytes of memory, and gives you a pointer to it, one that
>you can't (or shouldn't) change.
>
>Thus,
>
>char a[80];
>main()
>{
>  strcpy(a,"hello");
>}
>
>is okay, while
>
>char *a;
>main()
>{
>  strcpy(a,"hello");
>}
>
>will cause real problems, like overwriting your program or another task
>with the word "hello".  You'd have to do a malloc() or AllocMem() or
>something to have a safe place to put the "hello".
>
>So, is this right, or is my feeling of confusion justified?
>
>-- 
>Eric Kennedy
>ejkst@cisunx.UUCP


You are correct in your statements.  However, the I was addressing
the common practice of thinking of the symbol 'a' in the following
code:

char a[80]

as a pointer to the array, and using it as such.  While this works
most of the time, it is not 100% correct.

For example, in most instances, the following code will have
the same effect:

function1()
{
    char array[80];
    char *a;

    a = array;
    strcpy (a,"Hello");
}

and

function2()
{
    char array[80];

    strcpy(array,"Hello");
}

In both instances, "hello" will be placed into array[];
However, look at the definition of strcpy.  It requires
a char * for both its arguments.  the identifier 'array'
is not truly a char *, but can be used as such in this instance.

This common practice is fine normally, but there are a few times
that it can bite you.

I think (but don't know for sure), that the technical definition
of "array" in the above examples is really "&array[0]".

     -- Kevin --

Kevin Klop		{uunet|rutgers|amiga}!cbmvax!kevin
Commodore-Amiga, Inc.

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