Xref: utzoo comp.sources.d:2094 comp.lang.c:10101
Newsgroups: comp.sources.d,comp.lang.c
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Flex on MSDOS and C block structure
Message-ID: <1988May15.002127.413@utzoo.uucp>
Keywords: nested declarations flex msdos
Organization: U of Toronto Zoology
References: <4060@killer.UUCP>
Date: Sun, 15 May 88 00:21:27 GMT

>  ...  Does the ANSI standard (or
>  K&R for that matter) have anything to say about exiting a context and
>  reentering it saving (or not saving) the state of local variables?

All definitions of C that I'm aware of make it quite clear that the values
of uninitialized local variables are unknown when the block containing
them is entered, *regardless* of whether the block was executed before and
gave them a value then.  Old values go away when the block is exited.

> Might
>   the fact that this code seems to work almost everywhere imply that Unix
>   and VMS (AT&T derived?) C compilers allocate local variables on the
>   entry to the function, rather than entry to the block?...

Correct in general.  But it's not something one should depend on, of course.
Even if allocation is at function-entry time, clever compilers may well
re-use the space for something else after the block is exited.
-- 
NASA is to spaceflight as            |  Henry Spencer @ U of Toronto Zoology
the Post Office is to mail.          | {ihnp4,decvax,uunet!mnetor}!utzoo!henry