[Bug libstdc++/32422] New: Problem reading floats with exponent marker but no exponent

["kreckel at ginac dot de" <gcc-bugzilla at gcc dot gnu dot org>]

When reading malformed floats like "3.14e" using operator>>, it appears like
the e character is removed from the input stream but the fact that the stream
state does not signal that something went wrong.

$ cat lcast.cpp
#include <sstream>
#include <iostream>
using namespace std;

int main()
{
    stringstream buf;
    buf.str("1e");
    float r;
    buf >> r;
    cout << "float==" << r << endl;
    cout << "tellg()==" << buf.tellg() << endl;
    cout << "fail()==" << buf.fail() << endl;
}
$ g++ lcast.cpp  &&  ./a.out
float==1
tellg()==2
fail()==0

This was noticed in the context of the boost library. There,
boost::lexical_cast<float>("1e") silently return 1.0, which is surprising. E.g.
a compiler would reject float x = 1e saying "exponent has no digits" or
something along these lines.


-- 
           Summary: Problem reading floats with exponent marker but no
                    exponent
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kreckel at ginac dot de
 GCC build triplet: x86_64-suse-linux
  GCC host triplet: x86_64-suse-linux
GCC target triplet: x86_64-suse-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32422