Passing parameter pack to emplace stl function cause compilation bug

Question

According to the definition of emplace_back, void emplace_back (Args&&... args); is a variadic template function. So, I wrote the following:

#include <vector>

int main()
{
  std::vector<int> myvector2(10,0);
  myvector2.emplace_back(1,2,3,4,5,6);
}

The compiler complains:

g++ -std=c++0x stlstudy.cc
‘
Internal compiler error: Error reporting routines re-entered.
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-4.7/README.Bugs> for instructions.
Preprocessed source stored into /tmp/cc7q32tE.out file, please attach this to your bugreport.

And the OS alerts:

Sorry, Ubuntu 13.04 has experienced an internal error.

The /tmp/cc7q32tE.out filen is too long to post it here and maybe it will not help. Am I doing something wrong or is compilation bug? I don't get it.

After the comments and the bug report: jrok gives a very good explanation about why this happens. I used gcc 4.7, I reported the bug and I got the following response:

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.8.0

--- Comment #1 from Jonathan W***** <redi at gcc dot gnu.org> ---
Seems to be fixed for 4.8 already.

Answer 1

Internal compiler error is not your fault. Compilers are supposed to give a meaningful diagnostic in case of ill-formed input, not just crash on you.

However, the number and types of arguments of emplace_back must match one of the constructors of vector's value type. You have a vector of ints, so you can pass at most one argument that either has a matching type or is implicitly convertible to value_type. (You could leave argument list empty - that would construct the object using default constructor).

std::vector<int> v;
v.emplace_back(1);   // ok
v.emplace_back(1.0); // ok
v.emplace_back(1, 2); // not ok, there's no constructor for `int` that takes two ints

The purpose of emplace_back isn't to push multiple elements in the same statement (I got an impression that this is what you expected it to do - I thought the same a while ago) but to construct an element in place, forwarding the arguments to the constructor and avoiding copies).

Gcc 4.8. does error out, although the error message isn't particulalry helpul.