bug#21279: 24.4; (match-end 0) doesn't always return nil when previous string-match fails

bug#21279: 24.4; (match-end 0) doesn't always return nil when previous string-match fails

[Ernesto Alfonso]

(match-end 0) doesn't always return nil when previous string-match fails:


(progn
	 (string-match "a+" "aaa")
	 (match-end 0)
	 (string-match "a+" "bbb")
	 (match-end 0)) 

returns 3, should be nil:

"match-end is a built-in function in `search.c'.
[...]
Value is nil if SUBEXPth pair didn't match, or there were less than
  SUBEXP pairs.
  "

             



In GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.5)
 of 2015-03-07 on trouble, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11604000
System Description:	Debian GNU/Linux 8.1 (jessie)

Configured using:
 `configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.4/site-lisp:/usr/share/emacs/site-lisp
 --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.4/site-lisp:/usr/share/emacs/site-lisp
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars
 'CFLAGS=-g -O2 -fstack-protector-strong -Wformat
 -Werror=format-security -Wall' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-z,relro'

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Summary

Minor modes in effect:
  erc-list-mode: t
  erc-menu-mode: t
  erc-autojoin-mode: t
  erc-ring-mode: t
  erc-networks-mode: t
  erc-pcomplete-mode: t
  erc-track-mode: t
  erc-track-minor-mode: t
  erc-match-mode: t
  erc-button-mode: t
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  erc-stamp-mode: t
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  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<f2> c x e <f2> / / s-? C-g <f2> x e 1 M-1 2 n n n 
n M-f M-f : SPC x e c / s-? <f1> 1 <f2> 1 1 <f2> <f1> 
<f1> <f2> <f2> e <f1> s e t i t e m <return> <f1> c 
<f1> c e b b SPC s-G e x e s c s-? <up> <return> p 
p p 1 K c b b b b b b f b b b M-b s-3 u p c a s e SPC 
<f1> M-f <escape> M-b M-f f M-b j M-f j e n 1 n n x 
e s c s-? <up> <return> K K p p p n / / / / / / / s-: 
/ s-? <up> e n t e r SPC <return> 2 p n n n n n n n 
n e j s-? s e t i t e m SPC p r o m i s e <return> 
1 2 c 1 1 p e 1 n p n M-b n K x e s c 2 2 2 2 2 2 2 
2 2 1 1 1 n e j s-? o n <M-backspace> s e t i t e m 
SPC t r a n s a c t i o n SPC o n c o m p l e t e <return> 
p 1 p p 1 p 1 p p p p p p p p p p p p p n e j s-? <up> 
M-f C-f C-k o n SPC v a l u e <return> <f9> x i e c 
M-x r e p o r t <tab> <return> C-g x o C-g M-x r e 
p o r t - e m <tab> <return>

Recent messages:

now playing: /home/ealfonso/Music/ytdl/Billy Joel New York state of mind-ol0dPJdzm1M.mp3
count is 3 
debug-random-line
Saving file /home/ealfonso/repos/dotemacs/.emacs...
Wrote /home/ealfonso/repos/dotemacs/.emacs
count is 3  [2 times]
(Shell command succeeded with no output)
change: stopped (signal)

Quit [2 times]

Load-path shadows:
/home/ealfonso/repos/dotemacs/experimental/go-mode hides /home/ealfonso/repos/dotemacs/emacs_external_libraries/go-mode
/home/ealfonso/repos/dotemacs/experimental/dired-sort-menu hides /home/ealfonso/repos/dotemacs/emacs_external_libraries/dired-sort-menu
/usr/share/emacs/24.4/site-lisp/debian-startup hides /usr/share/emacs/site-lisp/debian-startup
/home/ealfonso/repos/dotemacs/experimental/dired hides /usr/share/emacs/24.4/lisp/dired
/home/ealfonso/repos/dotemacs/emacs_external_libraries/ls-lisp hides /usr/share/emacs/24.4/lisp/ls-lisp
/usr/share/emacs24/site-lisp/dictionaries-common/ispell hides /usr/share/emacs/24.4/lisp/textmodes/ispell
/usr/share/emacs/site-lisp/rst hides /usr/share/emacs/24.4/lisp/textmodes/rst
/usr/share/emacs24/site-lisp/dictionaries-common/flyspell hides /usr/share/emacs/24.4/lisp/textmodes/flyspell
/home/ealfonso/repos/dotemacs/emacs_external_libraries/emacsplanner/remember/remember hides /usr/share/emacs/24.4/lisp/textmodes/remember
/home/ealfonso/repos/dotemacs/emacs_external_libraries/cl-lib hides /usr/share/emacs/24.4/lisp/emacs-lisp/cl-lib

Features:
(shadow emacsbug erc-list erc-menu erc-join erc-ring erc-networks
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esh-var esh-io esh-cmd esh-opt esh-ext esh-proc esh-arg eldoc esh-groups
eshell esh-module esh-mode esh-util mail-extr nxml-uchnm rng-xsd
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nxml-outln nxml-rap nxml-util nxml-glyph nxml-enc xmltok tabify
sh-script smie executable macros mule-util ielm qp gnus-ml disp-table
nndraft nnmh nnfolder utf-7 gnutls nnimap parse-time utf7 netrc
gnus-agent gnus-srvr gnus-score score-mode nnvirtual gnus-msg gnus-art
mm-uu mml2015 mm-view mml-smime smime dig nntp gnus-cache gnus-sum nnoo
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gnus-range message rfc822 mml mml-sec mailabbrev gmm-utils mailheader
gnus-win gnus gnus-ems nnheader mail-utils tramp-sh smerge-mode
diff-mode diff pcmpl-unix files-x debug sql view dired-aux face-remap
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arc-mode archive-mode pp hyperspec browse-url loadhist auto-imports moz
edebug package epg-config matlab-load calfw-ical icalendar server
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text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
dbusbind gfilenotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 2397617 377103)
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bug#21279: 24.4; (match-end 0) doesn't always return nil when previous string-match fails

[Andreas Schwab]

Ernesto Alfonso <erjoalgo@gmail.com> writes:

> (match-end 0) doesn't always return nil when previous string-match fails:

A failing match doesn't set match-data.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

bug#21279: 24.4; (match-end 0) doesn't always return nil when previous string-match fails

[Ernesto Alfonso]

I see.

I think the documentation of match-end and others should be updated, though, since right now it is a little misleading:

"Value is nil if SUBEXPth pair didn't match, or there were less than
  SUBEXP pairs.
"

seems to suggest that if match fails, value should be nil. I was certaily confused.

Ernesto
Andreas Schwab <schwab@suse.de> writes:

> Ernesto Alfonso <erjoalgo@gmail.com> writes:
>
>> (match-end 0) doesn't always return nil when previous string-match fails:
>
> A failing match doesn't set match-data.
>
> Andreas.

bug#21279: 24.4; (match-end 0) doesn't always return nil when previous string-match fails

[Paul Eggert]

I updated the documentation along the lines that you suggested, as master commit 
7a68ebe0485d049a3fbbfd77d0ba5773e8e6ae87 and am marking this bug as done. 
Thanks for reporting it.