Ubuntu 12.04 GCC4.7啟用C++11

因為想用template aliases特性，必須要GCC4.7.

又不想編譯源代碼，所以按照下面的方法安裝。

1. sudo add-apt-repository ppa:Ubuntu-toolchain-r/test
2. sudo apt-get update
3. sudo apt-get install gcc-4.7
4. sudo apt-get install g++-4.7

如果Ubuntu 12.04 系統中存在多個版本的GCC，可以在CMake工程的頂層的CMakeLists.txt中配置：

1. cmake_minimum_required(VERSION 2.8.7)
2. set(CMAKE_C_COMPILER "/usr/bin/gcc-4.7")
3. set(CMAKE_CXX_COMPILER "/usr/bin/g++-4.7")
4. project (sample)
5. add_subdirectory(src bin)

1. chenshu@chenshu-beijing:~/work/research/tree/normal_tree/build$ cmake ..
2. -- The C compiler identification is GNU
3. -- The CXX compiler identification is GNU
4. -- Check for working C compiler: /usr/bin/gcc-4.7
5. -- Check for working C compiler: /usr/bin/gcc-4.7 -- works
6. -- Detecting C compiler ABI info
7. -- Detecting C compiler ABI info - done
8. -- Check for working CXX compiler: /usr/bin/g++-4.7
9. -- Check for working CXX compiler: /usr/bin/g++-4.7 -- works
10. -- Detecting CXX compiler ABI info
11. -- Detecting CXX compiler ABI info - done
12. -- Configuring done
13. -- Generating done
14. -- Build files have been written to: /home/chenshu/work/research/tree/normal_tree/build

不過我的方法不是CMake推薦的最佳方法，一共有三種方法可以參考：

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

1. How do I use a different compiler?
2. [edit] Method 1: use environment variables
3. 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.)
4. For example:
5. CC=gcc-4.2 CXX=/usr/bin/g++-4.2 cmake -G "Your Generator" path/to/your/source
6. [edit] Method 2: use cmake -D
7. Set the appropriate CMAKE_FOO_COMPILER variable(s) to a valid compiler name or full path on the command-line using cmake -D.
8. For example:
9. cmake -G "Your Generator" -D CMAKE_C_COMPILER=gcc-4.2 -D CMAKE_CXX_COMPILER=g++-4.2 path/to/your/source
10. [edit] Method 3 (avoid): use set()
11. 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).
12. For example:
13. set(CMAKE_C_COMPILER "gcc-4.2")
14. set(CMAKE_CXX_COMPILER "/usr/bin/g++-4.2")
16. project("YourProjectName")
17. [edit]

默認C++11是不啟用的。在src/CMakeLists.txt文件中加上這行：

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

cmake ..

make VERBOSE=1

你會看到編譯的g++命令後面帶上了：

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

現在成功了，享受C++11吧。

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