getting c++11 - compliant compiler - c++

Question

This all seems like a colossal mess.
All I want is a compiler that implements C++11, so I can use <chrono>. But I'm so confused from the very beginning.
Currently, I build programs by invoking G++, but when I check the version via $ g++ -v, I get:
gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build
2336.11.00)
What's going on? Am I using G++? GCC? LLVM? I don't even know. Are they the same thing?
So now I'm trying to build and download GCC 4.7 via gnu.org, but I have no idea what any of the guides are talking about. I've never seen so many acronyms for things I dont know.
Why is this so complicated? What's with all those versions, with some of them only implementing some parts of C++11 and not others?

Answer 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++.

Answer 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

Answer 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.