[Bug c++/58924] New: Non-member invocation of overload of operator<< when the first argument is a temporary of type std::stringstream

[Bug c++/58924] New: Non-member invocation of overload of operator<< when the first argument is a temporary of type std::stringstream

[sir_nawaz959 at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58924

            Bug ID: 58924
           Summary: Non-member invocation of overload of operator<< when
                    the first argument is a temporary of type
                    std::stringstream
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sir_nawaz959 at yahoo dot com

I'm using GCC-4.8.1 in C++11 Mode.

Consider this code,

#include <sstream>
#include <iostream>

int main()
{
    auto s = static_cast<std::stringstream&>(std::stringstream() << "XYZ" <<
"ABC").str();

    std::cout << s << std::endl;
}

Actual (incorrect) output:

XYZABC

The expected output is an address following by ABC, something like this:

0x400e83ABC


Because `std::stringstream()` is a temporary, so the first invocation of
`operator<<` must resolve to a member function (taking void* as argument) which
would print the address, and then the non-member function should be invoked for
the second `<<`.

Note that this works as expected when I don't use `-std=C++11` (of course, in
that case I use `std::string` instead of `auto`).

[Bug c++/58924] Non-member invocation of overload of operator<< when the first argument is a temporary of type std::stringstream

[fanael4 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58924

Fanael <fanael4 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fanael4 at gmail dot com

--- Comment #1 from Fanael <fanael4 at gmail dot com> ---
That's expected behavior AFAIU. 'operator<<(basic_ostream<charT, traits>&& os,
const T& x)' is a better match for const char[K] than
'basic_ostream<charT,traits>& basic_ostream<charT,traits>::operator<<(const
void* p)', hence the former gets called, which then forwards the arguments to
'operator<<(basic_ostream<charT, traits>&& os, const charT* x)'.

[Bug c++/58924] Non-member invocation of overload of operator<< when the first argument is a temporary of type std::stringstream

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58924

--- Comment #3 from Daniel Krügler <daniel.kruegler at googlemail dot com> ---
(In reply to Fanael from comment #1)
I agree with Fanael: It is supposed to be that way in C++11 because of the
provided stream-rvalue support via

template <class charT, class traits, class T>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>&& os, const T& x);
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Subject: [Bug rtl-optimization/58384] [4.9 regression] Runfail on spec2000/253.perlbmk if lto and pre-reload scheduler is used on x86 after r200133.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idX384

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2013-10-30
     Ever confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Is it maybe fixed by the fix for PR58831?  I can't seem to pattern match
the assembler generated by trunk with your description anymore.

[Bug libstdc++/58924] Non-member invocation of overload of operator<< when the first argument is a temporary of type std::stringstream

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58924

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
          Component|c++                         |libstdc++
         Resolution|---                         |INVALID

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is not a bug.

[Bug libstdc++/58924] Non-member invocation of overload of operator<< when the first argument is a temporary of type std::stringstream

[sir_nawaz959 at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58924

--- Comment #5 from Sarfaraz Nawaz <sir_nawaz959 at yahoo dot com> ---
(In reply to Fanael from comment #1)
> That's expected behavior AFAIU. 'operator<<(basic_ostream<charT, traits>&&
> os, const T& x)' is a better match for const char[K] than
> 'basic_ostream<charT,traits>& basic_ostream<charT,traits>::operator<<(const
> void* p)', hence the former gets called, which then forwards the arguments
> to 'operator<<(basic_ostream<charT, traits>&& os, const charT* x)'.


Oh. I didn't come across this overload. Great that they've added this.

Invalid bug.