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From: "alex-j-a at hotmail dot co.uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/64814] std::copy_n advances InputIterator one *less* time than necessary.
Date: Thu, 29 Jan 2015 21:06:00 -0000 [thread overview]
Message-ID: <bug-64814-4-zTtTtXJfAR@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-64814-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64814
--- Comment #9 from Anquietas <alex-j-a at hotmail dot co.uk> ---
(In reply to Jonathan Wakely from comment #8)
> N.B. libc++ changed its copy_n with
> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110221/039404.
> html and then libstdc++ did the same in PR 50119
I linked that bug report in the OP, but as it happens the behaviour is quite
interesting with std::istream_iterator<int> using an adaptation of the code I
pasted in OP:
int main() {
std::istringstream ss("1 2 3 4 5 6 7 8 9 0 1 2 ");
std::vector<int> output;
auto readIter = std::istream_iterator<int>(ss);
for (int i = 0; i < 3; ++i) {
output.clear();
auto inserter = std::back_inserter(output);
// Doesn't work - outputs 123415671890
std::copy_n(readIter, 4, inserter);
for (auto n : output)
std::cout << n;
}
}
However, in this case moving readIter's declaration inside the loop fixes it.
If we go back to the code in OP and do the same, it *doesn't* fix it and still
produces the same output in either case. At the very least, the current
implementation of copy_n appears to be inconsistent, depending on the type of
iterator used. The implementation I provided for copy_n in OP doesn't work for
the istream_iterator case though, and neither does the direct for loop
approach.
prev parent reply other threads:[~2015-01-29 21:06 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-27 3:49 [Bug libstdc++/64814] New: " alex-j-a at hotmail dot co.uk
2015-01-27 11:28 ` [Bug libstdc++/64814] " redi at gcc dot gnu.org
2015-01-27 16:06 ` redi at gcc dot gnu.org
2015-01-27 16:09 ` alex-j-a at hotmail dot co.uk
2015-01-27 16:18 ` redi at gcc dot gnu.org
2015-01-27 16:29 ` redi at gcc dot gnu.org
2015-01-27 16:40 ` alex-j-a at hotmail dot co.uk
2015-01-27 16:51 ` alex-j-a at hotmail dot co.uk
2015-01-27 17:06 ` redi at gcc dot gnu.org
2015-01-28 13:40 ` redi at gcc dot gnu.org
2015-01-29 21:06 ` alex-j-a at hotmail dot co.uk [this message]
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