[Bug libstdc++/45280] New: Stream parsing of digit-then-e (with no exponent) now fails
In past versions of the C++ standard library, if I piped a string like 59e
into a double, it would set the double to '59' and set position of the get
pointer to after the e. This meant I had to check if the last char read was an
'e' and if so, back up, but that was OK.
Something changed (and I wish I could tell you when, but I don't know--probably
in my upgrade from ubuntu 9.04 to 10.04) so now when I do the same thing, the
stream parser just gets confused, sets the 'fail' bit, and sets the double to
0. Here's a test program:
#include sstream
#include iostream
using namespace std;
int main(int argc, char** argv)
{
stringstream withx, withe;
withx 59x;
withe 59e;
double num;
char cc;
withx num;
cc = withx.get();
cout From the string '59x', the streamed number is num , and the
next character is ' cc ' endl;
withe num;
cc = withe.get();
cout From the string '59e', the streamed number is num , and the
next character is ' cc ' endl;
cout tellg: withe.tellg() endl;
cout tellp: withe.tellp() endl;
cout eof? withe.eof() endl;
cout fail? withe.fail() endl;
cout bad? withe.bad() endl;
}
which outputs:
From the string '59x', the streamed number is 59, and the next character is 'x'
From the string '59e', the streamed number is 0, and the next character is
'#65533;'
tellg: -1
tellp: -1
eof? 0
fail?1
bad?0
Now, ideally, parsing '59e' should behave exactly the same as parsing '59x'--it
would notice that there's no exponent, decide the 'e' wasn't part of the
number, back up, export '59', and the next result of 'get' would return 'e'.
But barring that, going back to the old behavior of not failing and returning
59, even if the get position is post-e, would be great.
I apologize for not testing this in more recent builds--I did check the
changelog and the list of bug fixes, and didn't find this in there, though I
certainly could have missed it.
--
Summary: Stream parsing of digit-then-e (with no exponent) now
fails
Product: gcc
Version: 4.4.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: lpsmith at u dot washington dot edu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45280
[Bug libstdc++/45280] Stream parsing of digit-then-e (with no exponent) now fails
--- Comment #2 from lpsmith at u dot washington dot edu 2010-08-13 20:22 --- Is the reasoning explained somewhere? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45280
[Bug libstdc++/45280] Stream parsing of digit-then-e (with no exponent) now fails
--- Comment #4 from lpsmith at u dot washington dot edu 2010-08-13 20:34 --- Yes, exactly! Which is why the 'e' should not be parsed at all unless there is an optional sign and a compulsory digit following it. The 'e' in general is not compulsory. '59' is a valid double. The context is that I am parsing (among other things) chemical reactions. It is perfectly valid to have something like: 2EtOH - EtOHX -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45280
[Bug libstdc++/45280] Stream parsing of digit-then-e (with no exponent) now fails
--- Comment #5 from lpsmith at u dot washington dot edu 2010-08-13 20:56 --- Followup: This still fails even if you're trying to pipe it into an integer and not a double. Integers, as per 22.2.3.1 in C++98, do not have an optional 'e' after them. (Though of course you could *cast* a floating point value to an integer.) Given that, I hope you won't mind if I reopen the bug. -- lpsmith at u dot washington dot edu changed: What|Removed |Added Status|RESOLVED|UNCONFIRMED Resolution|INVALID | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45280
[Bug libstdc++/45280] Stream parsing of digit-then-e (with no exponent) now fails
--- Comment #7 from lpsmith at u dot washington dot edu 2010-08-13 21:14 --- You're right! Sorry; I apparently jumped to a conclusion while testing (but I did test!) I still disagree that an 'e' with no digit following can be reasonably construed as part of an improperly-formatted float, and think it should instead be considered not part of the float at all, since properly-formatted floats have both the e and the digit. I think you are erring on the side of assuming an error when a valid interpretation exists. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45280
[Bug libstdc++/45280] Stream parsing of digit-then-e (with no exponent) now fails
--- Comment #9 from lpsmith at u dot washington dot edu 2010-08-13 21:40 --- Fair enough! I still disagree, but I guess my task now is to get Dinkumware and Roguewave to change their implementations, and come back. I don't suppose you'd be swayed by Microsoft? I didn't think so ;-) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45280
[Bug libstdc++/45280] Stream parsing of digit-then-e (with no exponent) now fails
--- Comment #10 from lpsmith at u dot washington dot edu 2010-08-13 21:41 --- Whoops, duh, dinkumware is ms. Never mind, it was a dumb joke anyway. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45280
