Ubuntu 12.04 GCC4.7启用C++11

因为想用template aliases特性，必须要GCC4.7.

又不想编译源代码，所以按照下面的方法安装。

sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt-get update
sudo apt-get install gcc-4.7
sudo apt-get install g++-4.7

如果系统中存在多个版本的GCC，可以在CMake工程的顶层的CMakeLists.txt中配置：

cmake_minimum_required(VERSION 2.8.7)
set(CMAKE_C_COMPILER "/usr/bin/gcc-4.7")
set(CMAKE_CXX_COMPILER "/usr/bin/g++-4.7")
project (sample)
add_subdirectory(src bin)

然后在build目录下执行cmake .. 可以看到：

chenshu@chenshu-beijing:~/work/research/tree/normal_tree/build$ cmake ..
-- The C compiler identification is GNU
-- The CXX compiler identification is GNU
-- Check for working C compiler: /usr/bin/gcc-4.7
-- Check for working C compiler: /usr/bin/gcc-4.7 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/g++-4.7
-- Check for working CXX compiler: /usr/bin/g++-4.7 -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/chenshu/work/research/tree/normal_tree/build

不过我的方法不是CMake推荐的最佳方法，一共有三种方法可以参考：

http://www.cmake.org/Wiki/CMake_FAQ#Method_3_.28avoid.29:_use_set.28.29

How do I use a different compiler?
[edit] Method 1: use environment variables
For C and C++, set the CC and CXX environment variables. This method is not guaranteed to work for all generators. (Specifically, if you are trying to set Xcode's GCC_VERSION, this method confuses Xcode.)
For example:
CC=gcc-4.2 CXX=/usr/bin/g++-4.2 cmake -G "Your Generator" path/to/your/source
[edit] Method 2: use cmake -D
Set the appropriate CMAKE_FOO_COMPILER variable(s) to a valid compiler name or full path on the command-line using cmake -D.
For example:
cmake -G "Your Generator" -D CMAKE_C_COMPILER=gcc-4.2 -D CMAKE_CXX_COMPILER=g++-4.2 path/to/your/source
[edit] Method 3 (avoid): use set()
Set the appropriate CMAKE_FOO_COMPILER variable(s) to a valid compiler name or full path in a list file using set(). This must be done before any language is set (ie before any project() or enable_language() command).
For example:
set(CMAKE_C_COMPILER "gcc-4.2")
set(CMAKE_CXX_COMPILER "/usr/bin/g++-4.2")

project("YourProjectName")
[edit]

默认C++11是不启用的。在src/CMakeLists.txt文件中加上这行：

SET(CMAKE_CXX_FLAGS "-std=c++11") # Add c++11 functionality

然后运行

cmake ..

make VERBOSE=1

你会看到编译的g++命令后面带上了：

 /usr/bin/g++-4.7    -std=c++11 

现在成功了，享受C++11吧。