Hi,
Please consider the following code:
$ cat bug.cpp
#include <iostream>
using namespace std;
void fun()
{
string dummy;
cin >> dummy;
}
int main()
{
cout << "FAIL = 0x" << hex << ios::failbit << endl;
cout << "EOF = 0x" << hex << ios::eofbit << endl;
cout << "BAD = 0x" << hex << ios::badbit << endl;
cin.exceptions(ios::eofbit | ios::failbit);
try {
fun();
}
catch (ios_base::failure&) {
cerr << "Failure caught!" << endl;
}
catch (...) {
cerr << "Failure uncaught! 0x" << hex << cin.rdstate() << endl;
}
return 0;
}
When this program is compiled and run on Linux, the exception gets caught:
$ uname -a
Linux iebdev11 3.10.0-862.14.4.el7.x86_64 #1 SMP Wed Sep 26 15:12:11 UTC 2018
x86_64 x86_64 x86_64 GNU/Linux
$ g++ --version
g++ (GCC) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ g++ -Wall bug.cpp -o bug
$ ./bug < /dev/null
FAIL = 0x4
EOF = 0x2
BAD = 0x1
Failure caught!
However, same commands on Cygwin, and the exception goes unhandled:
$ uname -a
CYGWIN_NT-10.0 NCBIPC9135 2.11.1(0.329/5/3) 2018-09-05 10:24 x86_64 Cygwin
$ gcc --version
gcc (GCC) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ g++ -Wall -o bug bug.cpp
$ ./bug < /dev/null
FAIL = 0x4
EOF = 0x2
BAD = 0x1
Failure uncaught! 0x6
We've seen this behavior before on Linux too, when the C++ ABI was changed
(w/GCC 5.x). I guess CYGWIN packages a version of C++ STDLIB whose ABI is
incompatible with default compiler settings.
Here's some explanation of what might be the culprit.
https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html says that:
> Using the default configuration options for GCC the default value of the
> macro is 1 which causes the new ABI to be active, so to use the old ABI you
> must explicitly define the macro to 0 before including any library headers.
> (Be aware that some GNU/Linux distributions configure GCC 5 differently so
> that the default value of the macro is 0 and users must define it to 1 to
> enable the new ABI.)
> One exception type does change when using the new ABI, namely
> std::ios_base::failure. This is necessary because the 2011 standard changed
> its base class from std::exception to std::system_error, which causes its
> layout to change. Exceptions due to iostream errors are thrown by a function
> inside libstdc++.so, so whether the thrown exception uses the old
> std::ios_base::failure type or the new one depends on the ABI that was active
> when libstdc++.so was built, not the ABI active in the user code that is
> using iostreams. This means that for a given build of GCC the type thrown is
> fixed. In current releases the library throws a special type that can be
> caught by handlers for either the old or new type, but for GCC 7.1, 7.2 and
> 7.3 the library throws the new std::ios_base::failure type, and for GCC 5.x
> and 6.x the library throws the old type. Catch handlers of type
> std::ios_base::failure will only catch the exceptions if using a newer
> release, or if the handler is compiled with the same ABI as the type thrown
> by the library. Handlers for std::exception will always catch iostreams
> exceptions, because the old and new type both inherit from std::exception.
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