getting c++11 - compliant compiler

Question 1

Here's the situation on OS X.

There are two C++ compilers installed by default.

[5:49pm][wlynch@watermelon ~] g++ --version
i686-apple-darwin11-llvm-g++-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)

[5:49pm][wlynch@watermelon ~] clang++ --version
Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn)

g++ is running llvm-gcc, which is the gcc frontend, and then the llvm backend.

clang++ is running clang, which is the clang frontend and then the llvm backend.

If you want a C++11 compiler on OS X without installing other packages, your only option is to use the clang compiler.

The flags necessary are:

clang++ -stdlib=libc++ -std=gnu++11

To describe the two flags I'm passing:

-stdlib=libc++ uses the libc++ standard library, instead of the gnu libstdc++. On OS X, the libc++ version has c++11 support. The gnu libstdc++ one does not.
-std=gnu++11 tells the compiler to support c++11 code features, like lambdas and enum class. You can also pass -std=c++11, which is similar, but does not enable some commonly expected gnu extensions.

Update for OS X 10.9: As of OS X Mavericks, both g++ and clang++ are actually using clang. The only difference, is that g++ will imply -stdlib=libstdc++ and clang++ will imply -stdlib=libc++. So, on Mavericks, if you'd like to use C++11, you can follow the above advice, or just do:

clang++ -std=gnu++11

Update for OS X 10.10: As of OS X Yosemite, g++ is still clang in disguise. However, neither uses libstdc++ by default anymore. Both are now on libc++.

Question 2

It sounds like you have Xcode 4.6 and the latest command line tools. This is from the release notes:

Important: The LLVM GCC compiler does not include the latest Objective-C and 
C++11 features. Xcode 4.6 is the last major Xcode release which includes the 
LLVM GCC compiler and the GDB debugger. Please migrate your projects to use the 
LLVM compiler and LLDB debugger…

I think you want to use c++ instead:

$ c++ -v
Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.2.0
Thread model: posix

Question 3

@sharth: The situation changed on the Mac quite significantly since the release of XCode 5.0. clang/clang++ are the default C/C++ compilers. They correspond to the LLVM version 3.3 I believe, and this version of clang++ is fully C++11-compliant. Note that clang++ --version will return a version number like "5.0.x" on the Mac but that refers to the XCode version.

I have been using the Apple clang++ in a C++11 project for months now and so far I have not seen any problems. There is absolutely no reason to use any other C++ compiler on the Mac just now :-)

The situation with GCC/G++ is not so rosy. The latest version of G++ (4.8.2) does implement most of the C++11 standard, however the standard library is not compliant! For instance, std::regex is not implemented in libstdc++, but you find this out only when you run your code and the regex constructors throw std::regex_error -s. (I found this out the hard way when trying to port the aforementioned little project to Linux.) The community believes full compliance will be achieved with the 4.9 release of G++. Until then you should use the Clang compilers on Linux as well.

I have no access to the latest Intel C++ compiler suite so have no idea how compliant icpc is.