This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: stderr vs. STDERR_FILENO

Gabriel Dos Reis wrote:

Jonathan Lennox <> writes:

| Zack Weinberg <zack at codesourcery dot com> writes:
| > For what it's worth I think this is primarily a documentation issue -
| | It just occured to me -- no, unfortunately, this is a correctness issue.
| | This C++ program is well-defined by the standard -- it invokes
| std::terminate, which invokes abort().
| | #include <cstdio>
| #include <stdexcept>
| | int main()
| {
| std::fclose(stderr);
| | throw std::runtime_error("Boom!");
| }
| | However, given a general-purpose C library which complies only with the
| requirements of the C/C++ standards, __gnu_cxx::__verbose_terminate_handler
| invokes undefined behavior on this program.

Which would strongly argue for keeping file descriptor 2.


As Jonathan pointed out, most (all?) stdio implementations will simply ignore writes to closed files. In which case, the behavior of the verose terminate handler, though technically undefined, will be correct.

Writing to file descriptor two after stderr has been closed is dangerous, independently of any standard. It might really screw up the system. Not just in an "that behavior is undefined, so the implementation can erase the disk" kind of way but in a "file descriptor two might be a special device" kind of way. In other words, it really might overwrite a disk partition.

If people are determined to avoid stdio, it would be better to get at the controlling tty and write the message there, in the same way that some kernels write messages about signals that kill the program. The controlling tty is at least very unlikely to be a raw disk partition.

The truly safe approach would be to make the verbose terminate handler a debugging option that users explicitly requested, rather than default behavior. I'm not necessarily arguing for that, but the safest route -- i.e, the route most likely to fully comply with the standard with the fewest surprises -- is just to do the one thing the standard requires: call std::abort.

Mark Mitchell
CodeSourcery, LLC
(916) 791-8304

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]