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| From | Kaz Kylheku <kaz@kylheku.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: about NULL as a parameter to a libc function |
| Date | 2011-10-28 20:17 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <20111028161052.465@kylheku.com> (permalink) |
| References | <14abde31-4573-45e7-bdaf-eb70b22741d7@z28g2000pro.googlegroups.com> |
On 2011-10-28, gaoqiang <gaoqiangscut@gmail.com> wrote: > a good function should deal with unwanted parameters. > > why memcpy,strcmp .etc ,these libc functions, do not > > accept NULL pointer ? called with NULL, just get segment This means that the funtions actually do accept the pointer and try to do what they are told: move memory to or from the null pointer! It's your virtual memory managment (CPU feature + operating system) that doesn't like the null pointer. If you dereference a null pointer to access memory, you will get this segfault, no matter what syntax or function you use. > fault. for efficiency ? No. It would be more efficient to just accept null inside the memcpy function (as is already the case in your implementation!) AND also not have the virtual memory management which catches the fault. Trapping null to a segfault requires extra circuitry which complicates the processor and introduces performance penalties (which are difficult to analyze, since they have to do with the access pattern to pages, and the replacement strategy of entries the translation cache.)
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about NULL as a parameter to a libc function gaoqiang <gaoqiangscut@gmail.com> - 2011-10-28 01:49 -0700
Re: about NULL as a parameter to a libc function Mark Bluemel <mark_bluemel@pobox.com> - 2011-10-28 10:14 +0100
Re: about NULL as a parameter to a libc function gaoqiang <gaoqiangscut@gmail.com> - 2011-10-28 03:22 -0700
Re: about NULL as a parameter to a libc function Mark Bluemel <mark_bluemel@pobox.com> - 2011-10-28 11:29 +0100
Re: about NULL as a parameter to a libc function Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-10-29 07:08 +0000
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-10-28 07:05 -0400
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-28 14:15 -0700
Re: about NULL as a parameter to a libc function gordonb.4o15x@burditt.org (Gordon Burditt) - 2011-10-28 16:36 -0500
Re: about NULL as a parameter to a libc function Robert Wessel <robertwessel2@yahoo.com> - 2011-10-28 17:30 -0500
Re: about NULL as a parameter to a libc function jgharston <jgh@arcade.demon.co.uk> - 2011-10-31 10:40 -0700
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-10-28 22:32 +0000
Re: about NULL as a parameter to a libc function Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-29 06:20 -0700
Re: about NULL as a parameter to a libc function "BartC" <bc@freeuk.com> - 2011-10-29 15:40 +0100
Re: about NULL as a parameter to a libc function Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-30 08:05 -0700
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-28 14:13 -0700
Re: about NULL as a parameter to a libc function Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-10-29 15:11 +0300
Re: about NULL as a parameter to a libc function Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-29 06:41 -0700
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-29 11:29 -0700
Re: about NULL as a parameter to a libc function Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-10-28 02:36 -0700
Re: about NULL as a parameter to a libc function Mike Manilone <mike@laptop.mike> - 2011-10-28 12:58 +0000
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-10-28 11:00 -0400
Re: about NULL as a parameter to a libc function Kenneth Brody <kenbrody@spamcop.net> - 2011-11-03 11:13 -0400
Re: about NULL as a parameter to a libc function Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-29 06:37 -0700
Re: about NULL as a parameter to a libc function Kenneth Brody <kenbrody@spamcop.net> - 2011-11-03 11:00 -0400
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-11-03 12:54 -0400
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-11-03 17:08 +0000
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-11-03 13:18 -0400
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-11-03 17:28 +0000
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-11-03 13:48 -0400
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-11-03 17:55 +0000
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-11-03 14:12 -0400
Re: about NULL as a parameter to a libc function blp@cs.stanford.edu (Ben Pfaff) - 2011-11-03 11:22 -0700
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-11-03 14:28 -0400
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-11-03 19:47 +0000
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-11-03 16:19 -0400
Re: about NULL as a parameter to a libc function Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-24 22:13 -0800
Re: about NULL as a parameter to a libc function Ike Naar <ike@sverige.freeshell.org> - 2011-11-03 18:20 +0000
Re: about NULL as a parameter to a libc function Ike Naar <ike@sverige.freeshell.org> - 2011-11-03 18:34 +0000
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-11-03 19:49 +0000
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-11-03 16:21 -0400
Re: about NULL as a parameter to a libc function Ike Naar <ike@iceland.freeshell.org> - 2011-11-03 22:19 +0000
Re: about NULL as a parameter to a libc function Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-24 22:17 -0800
Re: about NULL as a parameter to a libc function Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-24 21:19 -0800
Re: about NULL as a parameter to a libc function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-10-28 14:26 +0100
Re: about NULL as a parameter to a libc function Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-10-28 12:46 -0600
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-28 14:19 -0700
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-28 16:37 -0700
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-10-28 07:22 -0400
Re: about NULL as a parameter to a libc function Kenneth Brody <kenbrody@spamcop.net> - 2011-11-03 10:40 -0400
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-11-03 15:10 +0000
Re: about NULL as a parameter to a libc function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-11-04 03:03 +0000
Re: about NULL as a parameter to a libc function Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-10-28 08:42 -0400
Re: about NULL as a parameter to a libc function "io_x" <a@b.c.invalid> - 2011-10-28 16:31 +0200
Re: about NULL as a parameter to a libc function "BartC" <bc@freeuk.com> - 2011-10-28 20:29 +0100
Re: about NULL as a parameter to a libc function Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-10-29 14:49 +0300
Re: about NULL as a parameter to a libc function Ike Naar <ike@sverige.freeshell.org> - 2011-10-29 13:41 +0000
Re: about NULL as a parameter to a libc function John Gordon <gordon@panix.com> - 2011-10-28 19:53 +0000
Re: about NULL as a parameter to a libc function "BartC" <bc@freeuk.com> - 2011-10-28 21:13 +0100
Re: about NULL as a parameter to a libc function John Gordon <gordon@panix.com> - 2011-10-28 20:33 +0000
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-10-28 16:56 -0400
Re: about NULL as a parameter to a libc function blp@cs.stanford.edu (Ben Pfaff) - 2011-10-28 14:30 -0700
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-10-28 16:45 -0400
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-28 15:35 -0700
Re: about NULL as a parameter to a libc function "BartC" <bc@freeuk.com> - 2011-10-29 13:00 +0100
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-29 11:26 -0700
Re: about NULL as a parameter to a libc function "BartC" <bc@freeuk.com> - 2011-10-29 20:24 +0100
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-29 14:03 -0700
Re: about NULL as a parameter to a libc function Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-29 07:30 -0700
Re: about NULL as a parameter to a libc function Kenneth Brody <kenbrody@spamcop.net> - 2011-11-03 11:26 -0400
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-11-03 12:59 -0400
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-11-03 13:42 -0700
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-10-28 20:17 +0000
Re: about NULL as a parameter to a libc function Richard Damon <news.x.richarddamon@xoxy.net> - 2011-10-28 18:51 -0400
Re: about NULL as a parameter to a libc function Nobody <nobody@nowhere.com> - 2011-10-28 21:40 +0100
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-10-28 17:09 -0400
Re: about NULL as a parameter to a libc function Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-10-29 15:03 +0300
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-10-29 09:42 -0400
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-10-28 21:18 +0000
Re: about NULL as a parameter to a libc function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-10-28 23:30 +0100
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-28 15:37 -0700
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-10-28 23:47 +0000
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-10-28 17:13 -0700
Re: about NULL as a parameter to a libc function Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-10-29 04:31 +0100
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-10-29 05:42 +0000
Re: about NULL as a parameter to a libc function Seebs <usenet-nospam@seebs.net> - 2011-10-30 17:22 +0000
Re: about NULL as a parameter to a libc function Patrick Scheible <kkt@zipcon.net> - 2011-10-30 23:43 -0700
Re: about NULL as a parameter to a libc function Robert Wessel <robertwessel2@yahoo.com> - 2011-10-31 05:31 -0500
Re: about NULL as a parameter to a libc function Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-10-31 12:42 +0200
Re: about NULL as a parameter to a libc function Robert Wessel <robertwessel2@yahoo.com> - 2011-10-31 13:11 -0500
Re: about NULL as a parameter to a libc function Seebs <usenet-nospam@seebs.net> - 2011-10-31 17:18 +0000
Re: about NULL as a parameter to a libc function Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-29 07:32 -0700
Re: about NULL as a parameter to a libc function jacob navia <jacob@spamsink.net> - 2011-10-28 23:41 +0200
Re: about NULL as a parameter to a libc function Kaz Kylheku <kaz@kylheku.com> - 2011-10-28 22:42 +0000
Re: about NULL as a parameter to a libc function jacob navia <jacob@spamsink.net> - 2011-10-29 10:09 +0200
Re: about NULL as a parameter to a libc function Nobody <nobody@nowhere.com> - 2011-10-29 10:11 +0100
Re: about NULL as a parameter to a libc function Angel <angel+news@spamcop.net> - 2011-10-29 09:42 +0000
Re: about NULL as a parameter to a libc function jacob navia <jacob@spamsink.net> - 2011-10-29 16:17 +0200
Re: about NULL as a parameter to a libc function Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-29 07:39 -0700
Re: about NULL as a parameter to a libc function jacob navia <jacob@spamsink.net> - 2011-10-29 19:29 +0200
Re: about NULL as a parameter to a libc function "io_x" <a@b.c.invalid> - 2011-10-29 20:25 +0200
Re: about NULL as a parameter to a libc function Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-10-30 08:14 -0700
Re: about NULL as a parameter to a libc function ImpalerCore <jadill33@gmail.com> - 2011-10-31 18:30 -0700
Re: about NULL as a parameter to a libc function Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-24 18:21 -0800
Re: about NULL as a parameter to a libc function Kenneth Brody <kenbrody@spamcop.net> - 2011-11-03 11:31 -0400
Re: about NULL as a parameter to a libc function Keith Thompson <kst-u@mib.org> - 2011-11-03 13:45 -0700
Re: about NULL as a parameter to a libc function Jonathan Leffler <jleffler@earthlink.net> - 2011-10-29 23:41 -0700
Re: about NULL as a parameter to a libc function James Kuyper <jameskuyper@verizon.net> - 2011-10-30 07:13 -0400
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