http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58395
Bug ID: 58395
Summary: Undefined behavior vs. exception
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: frankhb1989 at gmail dot com
Several operations are undefined because they failed to meet required
behavior(ISO C++11 [defns.required.behavior]) at runtime. Currently libstdc++
throw exceptions for them. For example, when object of type std::string being
initialized using a null pointer value, an exception of type std::logic_error
is thrown by basic_string<char>::_S_construct. That's nothing wrong for
libstdc++ on conformance, because an implementation is free to do anything when
the behavior is undefined. However, this behavior is somewhat confusing for
users not so familiar with the standard. I suggest 2 options for future
releases of libstdc++:
1. Make the type of exceptions specific(i.e. as a documented feature),
distinguishable with other exceptions required to be thrown by the standard. It
can be a type derived from std::logic_error, as an extension.
2. Make the implementation-defined result of what() specific and
distinguishable, e.g. some prefix to indicate the exception is not mandated.
This is not only good for manually distinguishing UB, but also beneficial for
tests on conformance/portability of user programs.
