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| From | David Brown <david.brown@hesbynett.no> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: local arrays and stack |
| Date | 2015-03-25 21:42 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <mev6il$eav$1@dont-email.me> (permalink) |
| References | (16 earlier) <merf4a$uam$1@dont-email.me> <merksa$ko5$1@dont-email.me> <meumeh$3pd$1@dont-email.me> <meuogd$dge$1@dont-email.me> <mev0uh$kf3$1@dont-email.me> |
On 25/03/15 20:06, Bartc wrote: > On 25/03/2015 16:42, David Brown wrote: >> On 25/03/15 17:07, Bartc wrote: > >>> Suppose a function has input consisting two strings of given lengths M >>> and N, and it needs to concatenate them into a composite work string of >>> length M+N before any further processing, then that composite string is >>> discarded. >>> >>> It sounds very appealing to just define: >>> >>> char workstring[M+N+1]; >>> >>> except that M could be a million or a billion. > >> A fancy compiler that puts local data on the heap will not protect you >> from bad software design! > > What bad software design? It is declaring 'int array[N];' without being > pretty certain that N is within reasonable range, that is bad design. /Exactly/ the point - doing /anything/ with /any/ data is bad design if you require certain properties but don't know that these hold. If a stack size of 8 MB is a reasonable limit for your target systems, then it is bad design to allocate an array on the stack that could take you over that limit. But that is no different from any other checks or limits on incoming data - and a compiler will not make your program safe, reliable, or well-designed by deciding to put the array on the heap instead of the stack. > > (In fact, I didn't realise until this thread that VLAs were so unsafe. > You know about the usually remote risks of stack overflow when some > recursive algorithm goes out of control, but with VLAs you don't even > need to call one function, just declaring an array in the middle of > main() could be enough to bring down an application!) > VLA's are not unsafe. Allocating an unreasonable amount of data (from any storage) is unsafe. Working with unknown quantities without checking them is unsafe. Overflowing buffers is unsafe. Undefined behaviour is unsafe. In general, writing bad code is unsafe. But using a tool such as VLA's on the stack, or fixed-size arrays on the stack, is perfectly safe as long as you use them properly. And since stack-allocated arrays will be deallocated automatically, you could argue that they are less error-prone than heap allocated data as there is no risk of leaks.
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local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-22 01:51 -0700
local arrays and stack asetofsymbols@gmail.com - 2015-03-22 02:23 -0700
Re: local arrays and stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-22 13:22 -0700
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 01:55 -0700
Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-22 15:07 -0700
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 01:50 -0700
Re: local arrays and stack Robert Wessel <robertwessel2@yahoo.com> - 2015-03-23 04:26 -0500
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 06:53 -0700
Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 07:29 -0700
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 08:34 -0700
Re: local arrays and stack Robert Wessel <robertwessel2@yahoo.com> - 2015-03-23 19:57 -0500
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-24 04:01 -0700
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-24 04:37 -0700
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 13:04 +0100
Re: local arrays and stack glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-03-24 17:29 +0000
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 20:01 +0100
Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 08:24 -0700
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 08:42 -0700
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 16:07 +0000
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 09:15 -0700
Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 09:16 -0700
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 16:34 +0000
Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 10:12 -0700
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 17:44 +0000
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 11:47 -0700
Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 12:06 -0700
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 20:25 +0000
Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 14:10 -0700
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-23 22:22 +0000
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 23:57 -0700
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 10:28 +0100
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-24 10:44 +0000
Re: local arrays and stack Martin Shobe <martin.shobe@yahoo.com> - 2015-03-24 06:38 -0500
Re: local arrays and stack Martin Shobe <martin.shobe@yahoo.com> - 2015-03-24 09:57 -0500
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 13:22 +0100
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-25 16:07 +0000
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 17:42 +0100
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-25 19:06 +0000
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-25 12:26 -0700
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-25 13:20 -0700
Re: local arrays and stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-25 12:28 -0700
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 21:45 +0100
Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-25 12:50 -0700
Re: local arrays and stack Bartc <bc@freeuk.com> - 2015-03-25 22:33 +0000
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 23:57 +0100
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 21:42 +0100
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-25 09:55 -0700
Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-25 12:36 -0700
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-25 13:04 -0700
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-25 21:52 +0100
Re: local arrays and stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-25 15:18 -0700
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-26 00:02 +0100
Re: local arrays and stack Melzzzzz <mel@zzzzz.com> - 2015-03-26 00:47 +0100
Re: local arrays and stack Mel <mel@zzzzz.com> - 2015-03-24 14:58 +0100
Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-24 06:58 -0700
Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 14:34 -0700
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 10:16 +0100
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 09:55 +0100
Re: local arrays and stack Noob <root@127.0.0.1> - 2015-03-24 10:23 +0100
Re: local arrays and stack Tim Rentsch <txr@alumni.caltech.edu> - 2015-03-24 12:18 -0700
Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-24 13:42 -0700
Re: local arrays and stack Tim Rentsch <txr@alumni.caltech.edu> - 2015-03-25 08:47 -0700
Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 09:32 -0700
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-23 09:57 -0700
Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 10:37 -0700
Re: local arrays and stack Xcott Craver <xcottcraver@gmail.com> - 2015-03-23 10:49 -0700
Re: local arrays and stack Keith Thompson <kst-u@mib.org> - 2015-03-23 12:48 -0700
Re: local arrays and stack jt@toerring.de (Jens Thoms Toerring) - 2015-03-23 22:29 +0000
Re: local arrays and stack James Kuyper <jameskuyper@verizon.net> - 2015-03-23 19:03 -0400
Re: local arrays and stack jt@toerring.de (Jens Thoms Toerring) - 2015-03-23 23:36 +0000
Re: local arrays and stack fir <profesor.fir@gmail.com> - 2015-03-24 02:17 -0700
Re: local arrays and stack Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-03-23 11:56 -0700
Re: local arrays and stack Robert Wessel <robertwessel2@yahoo.com> - 2015-03-23 20:00 -0500
Re: local arrays and stack David Brown <david.brown@hesbynett.no> - 2015-03-24 10:39 +0100
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