Xref: utzoo comp.unix.xenix:2583 comp.sources.d:2380
Path: utzoo!attcan!uunet!sco!rosso
From: rosso@sco.COM (Ross Oliver)
Newsgroups: comp.unix.xenix,comp.sources.d
Subject: Re: tgetent core dump on sco xenix
Summary: Aren't segments fun?
Keywords: tgetent,core dump,sco,xenix,large model
Message-ID: <701@nod2sco>
Date: 2 Jul 88 06:48:21 GMT
References: <54@libove.UUCP>
Distribution: comp
Organization: SCO Technical Support
Lines: 34

In article <54@libove.UUCP> Jay Libove illistrates the single most
common mistake in large-model 286 programs.  The example he gives,
when compiled using "cc -M2l..." will dump core on execution:

>#include <stdio.h>
>#include <sgtty.h>
>
>main()
>	{
>	char	buffer[1024];
>
>	printf("%d\n",tgetent(buffer,getenv("TERM")));
>	};

Note that the return value of getenv() is not declared, therefore,
the compiler assumes int.  However, tgetent is expecting a char *,
and in large-model 286 programs, int != char *.  So, when main()
calls tgetent, it passes only two of the four bytes returned by
getenv().  tgetent picks up garbage data as the other two bytes,
and (suprise!) a segmentation violation results.  How can this be
fixed?  With the following declaration:

	char *getenv();

Here are a few tips to avoid problems like this in large-model
286 programs:

    - Declare your functions' return values.
    - Don't use "0" to mean NULL ( i.e. (char *)0 ).
    - Don't interchange ints and pointers, or longs and pointers.


Ross Oliver
SCO Technical Support