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* [Bug libstdc++/94749] New: std::istream::ignore discards too many characters
@ 2020-04-24 17:12 serpent7776 at gmail dot com
2020-04-25 14:42 ` [Bug libstdc++/94749] " redi at gcc dot gnu.org
` (9 more replies)
0 siblings, 10 replies; 11+ messages in thread
From: serpent7776 at gmail dot com @ 2020-04-24 17:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
Bug ID: 94749
Summary: std::istream::ignore discards too many characters
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: serpent7776 at gmail dot com
Target Milestone: ---
Created attachment 48369
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48369&action=edit
full source example
The following code results in '=' assigned to c when using libstdc++, but '+'
is assigned when using libc++, I believe libc++ is correct here
std::stringstream s(" +=");
char c;
s.ignore(1, '+');
s >> c;
Tested this on godbolt with newest gcc and locally on FreeBSD with gcc7
(command: g++7 -Wall -Wextra -pedantic test.cpp)
https://godbolt.org/z/yS5je8
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
@ 2020-04-25 14:42 ` redi at gcc dot gnu.org
2020-04-27 9:53 ` redi at gcc dot gnu.org
` (8 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: redi at gcc dot gnu.org @ 2020-04-25 14:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2020-04-25
Ever confirmed|0 |1
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
2020-04-25 14:42 ` [Bug libstdc++/94749] " redi at gcc dot gnu.org
@ 2020-04-27 9:53 ` redi at gcc dot gnu.org
2020-05-29 20:14 ` serpent7776 at gmail dot com
` (7 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: redi at gcc dot gnu.org @ 2020-04-27 9:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |redi at gcc dot gnu.org
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It looks like the bug is that when we have finished ignoring we assume that if
the next char is the delimiter, then that must be why we stopped, and so we
ignore that as well. But if we stopped because we reached the specified number
of characters, then whether the next char is the delimiter is irrelevant.
Shouldn't be hard to fix.
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
2020-04-25 14:42 ` [Bug libstdc++/94749] " redi at gcc dot gnu.org
2020-04-27 9:53 ` redi at gcc dot gnu.org
@ 2020-05-29 20:14 ` serpent7776 at gmail dot com
2020-05-29 20:29 ` redi at gcc dot gnu.org
` (6 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: serpent7776 at gmail dot com @ 2020-05-29 20:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
--- Comment #2 from serpent7776 at gmail dot com ---
any update?
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
` (2 preceding siblings ...)
2020-05-29 20:14 ` serpent7776 at gmail dot com
@ 2020-05-29 20:29 ` redi at gcc dot gnu.org
2020-06-11 17:41 ` cvs-commit at gcc dot gnu.org
` (5 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: redi at gcc dot gnu.org @ 2020-05-29 20:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I have a patch but was waiting until after the GCC 11 release.
I'll look into it next week.
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
` (3 preceding siblings ...)
2020-05-29 20:29 ` redi at gcc dot gnu.org
@ 2020-06-11 17:41 ` cvs-commit at gcc dot gnu.org
2020-06-11 17:43 ` redi at gcc dot gnu.org
` (4 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2020-06-11 17:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:
https://gcc.gnu.org/g:b32eea9c0c25a03e77170675abc4e4bcab6d2b3b
commit r11-1238-gb32eea9c0c25a03e77170675abc4e4bcab6d2b3b
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Jun 11 18:41:37 2020 +0100
libstdc++: Fix istream::ignore discarding too many chars (PR 94749)
The current code assumes that if the next character in the stream is
equal to the delimiter then we stopped because we saw that delimiter,
and so discards it. But in the testcase for the PR we stop because we
reached the maximum number of characters, and it's coincidence that the
next character equals the delimiter. We should not discard the next
character in that case.
The fix is to check that we haven't discarded __n characters already,
instead of checking whether the next character equals __delim. Because
we've already checked for EOF, if we haven't discarded __n yet then we
know we stopped because we saw the delimiter. On the other hand, if the
next character is the delimiter we don't know if that's why we stopped.
PR libstdc++/94749
* include/bits/istream.tcc (basic_istream::ignore(streamsize,
CharT)):
Only discard an extra character if we didn't already reach the
maximum number.
* src/c++98/istream.cc (istream::ignore(streamsiz, char))
(wistream::ignore(streamsize, wchar_t)): Likewise.
* testsuite/27_io/basic_istream/ignore/char/94749.cc: New test.
* testsuite/27_io/basic_istream/ignore/wchar_t/94749.cc: New test.
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
` (4 preceding siblings ...)
2020-06-11 17:41 ` cvs-commit at gcc dot gnu.org
@ 2020-06-11 17:43 ` redi at gcc dot gnu.org
2020-06-11 20:03 ` serpent7776 at gmail dot com
` (3 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: redi at gcc dot gnu.org @ 2020-06-11 17:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed in master. I'll keep the bug open as I will probably backport the fix.
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
` (5 preceding siblings ...)
2020-06-11 17:43 ` redi at gcc dot gnu.org
@ 2020-06-11 20:03 ` serpent7776 at gmail dot com
2020-07-09 21:34 ` redi at gcc dot gnu.org
` (2 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: serpent7776 at gmail dot com @ 2020-06-11 20:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
--- Comment #6 from serpent7776 at gmail dot com ---
thanks
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
` (6 preceding siblings ...)
2020-06-11 20:03 ` serpent7776 at gmail dot com
@ 2020-07-09 21:34 ` redi at gcc dot gnu.org
2020-07-13 11:26 ` cvs-commit at gcc dot gnu.org
2021-04-19 10:40 ` redi at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: redi at gcc dot gnu.org @ 2020-07-09 21:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The fix is actually not right, it fails to discard the delimiter if it occurs
after ignoring more than numeric_limits<streamsize>::max() characters.
I have a fix for that though.
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
` (7 preceding siblings ...)
2020-07-09 21:34 ` redi at gcc dot gnu.org
@ 2020-07-13 11:26 ` cvs-commit at gcc dot gnu.org
2021-04-19 10:40 ` redi at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2020-07-13 11:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:
https://gcc.gnu.org/g:ba8fe4b4832e30277f2e4a73b5d35b2e55074d07
commit r11-2054-gba8fe4b4832e30277f2e4a73b5d35b2e55074d07
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Jul 13 10:26:39 2020 +0100
libstdc++: Fix istream::ignore exit conditions (PR 94749, PR 96161)
My previous fix for PR 94749 did fix the reported case, so that the next
character is not discarded if it happens to equal the delimiter when __n
characters have already been read. But it introduced a new bug, which is
that the delimiter character would *not* be discarded if the number of
characters discarded is numeric_limits<streamsize>::max() or more before
reaching the delimiter.
The new bug happens because I changed the code to check _M_gcount < __n.
But when __n == numeric_limits<streamsize>::max() that is false, and so
we don't discard the delimiter. It's not sufficient to check for the
delimiter when the __large_ignore condition is true, because there's an
edge case where the delimiter is reached when _M_gcount == __n and so
we break out of the loop without setting __large_ignore.
PR 96161 is a similar bug to the original PR 94749 report, where eofbit
is set after discarding __n characters if there happen to be no more
characters in the stream.
This patch fixes both cases (and the regression) by checking different
conditions for the __n == max case and the __n < max case. For the
former case, we know that we must have either reached the delimiter or
EOF, and the value of _M_gcount doesn't matter (except to avoid integer
overflow). For the latter case we need to check _M_gcount first and only
set eofbit or discard the delimiter if it didn't reach __n. For the
latter case overflow can't happen because _M_gcount <= __n < max.
libstdc++-v3/ChangeLog:
PR libstdc++/94749
PR libstdc++/96161
* include/bits/istream.tcc (basic_istream::ignore(streamsize))
[n == max]: Check overflow conditions on _M_gcount. Rely on
the fact that either EOF or the delimiter was reached.
[n < max]: Check _M_gcount < n before checking for EOF or
delimiter.
(basic_istream::ignore(streamsize, char_type): Likewise.
* src/c++98/compatibility.cc (istream::ignore(streamsize))
(wistream::ignore(streamsize)): Likewise.
* src/c++98/istream.cc (istream::ignore(streamsize, char_type))
(wistream::ignore(streamsize, char_type)): Likewise.
* testsuite/27_io/basic_istream/ignore/char/94749.cc: Check that
delimiter is discarded if the number of characters ignored
doesn't fit in streamsize.
* testsuite/27_io/basic_istream/ignore/wchar_t/94749.cc:
Likewise.
* testsuite/27_io/basic_istream/ignore/char/96161.cc: New test.
* testsuite/27_io/basic_istream/ignore/wchar_t/96161.cc: New test.
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug libstdc++/94749] std::istream::ignore discards too many characters
2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
` (8 preceding siblings ...)
2020-07-13 11:26 ` cvs-commit at gcc dot gnu.org
@ 2021-04-19 10:40 ` redi at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: redi at gcc dot gnu.org @ 2021-04-19 10:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|redi at gcc dot gnu.org |unassigned at gcc dot gnu.org
Status|ASSIGNED |NEW
^ permalink raw reply [flat|nested] 11+ messages in thread
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2020-04-24 17:12 [Bug libstdc++/94749] New: std::istream::ignore discards too many characters serpent7776 at gmail dot com
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2020-04-27 9:53 ` redi at gcc dot gnu.org
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