Xref: utzoo comp.unix.questions:10100 comp.unix.wizards:12159
Path: utzoo!attcan!uunet!husc6!rutgers!att!ulysses!andante!alice!debra
From: debra@alice.UUCP (Paul De Bra)
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Re: alloca problem?
Keywords: alloca stack 386 sysv
Message-ID: <8393@alice.UUCP>
Date: 5 Nov 88 18:26:29 GMT
References: <17026@santra.UUCP>
Reply-To: debra@alice.UUCP ()
Organization: AT&T, Bell Labs
Lines: 42

In article <17026@santra.UUCP> hsu@santra.UUCP (Heikki Suonsivu) writes:
]Why this fails,
]
]huu(name)
]	char *name;
]{
]	char *d;
]
]	d = strcpy(alloca(strlen(name) + 1), name);
]
]	....
]}
]
]but this works?
]
]huu(name)
]	char *name;
]{
]	char *d;
]
]	d = alloca(strlen(name) + 1);
]	strcpy(d, name);
]
]	....
]}
]
This is not a problem of your Unix but of your program. Alloca does some
messing around with the stack. When you call it while you are pushing
arguments on the stack, you get in trouble. What I think is happening is
that name gets pushed on the stack, and then the alloca call moves the
stack pointer causing strcpy to go look for "name" in a different place.

The second example works because you first modify the stack and then
start pushing the arguments on the stack.
I am not saying that the first example won't work on any system (that has
alloca) but is is bad practice.

Paul.
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