安装依赖：
sudo apt-get install libncurses5-dev
sudo apt-get install build-essential cmake
sudo apt-get install python-dev python3-dev
sudo apt-get install libgmp-dev libmpfr-dev libmpc-dev libisl-dev libcloog-isl-dev zlib1g-dev
sudo apt-get install autogen
sudo apt-get install libclang-dev
升级CMake（可选）：
wget https://cmake.org/files/v3.5/cmake-3.5.2.tar.gz
tar xvf cmake-3.5.2.tar.gz
cd cmake-3.5.2
./bootstrap --prefix=/usr
make
sudo make install
升级GCC到4.9.2（如果你的gcc版本<=4.8）：
wget ftp://ftp.gnu.org/gnu/gcc/gcc-4.9.2/gcc-4.9.2.tar.gz
cd gcc-4.9.2
./configure --prefix=/opt/gcc-4.9.2 --enable-languages=c,c++ --disable-multilib --disable-bootstrap --with-system-zlib
make && make check
sudo make install
这样在/opt目录下就生成gcc4.9.2目录。
删除当前的gcc（可选）：
sudo apt-get remove gcc
创建软连接到bin文件夹：
sudo rm /usr/bin/gcc /usr/bin/g++
sudo ln -s /opt/gcc-4.9.2/bin/gcc /usr/bin/gcc
sudo ln -s /opt/gcc-4.9.2/bin/g++ /usr/bin/g++
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安装YCM插件的时候会提示"requires Vim compiled with Python (2.6+ or 3.3+) support."
网上有两种办法可以解决，但是我用第一种方法失败了，第二种方案可行！
方法一：
自己编译VIM：
git clone https://github.com/vim/vim.git
cd vim
git pull
配置python支持，否则在
./configure --enable-multibyte --enable-pythoninterp=yes
编译：
cd src
make distclean # if you build Vim before
make
sudo make install
方法二：
sudo add-apt-repository ppa:jonathonf/vim
sudo apt-get update
sudo apt-get install vim-nox-py2
sudo mv /usr/local/bin/vim /usr/local/bin/vim.old
sudo ln -s /usr/bin/vim.nox-py2 /usr/local/bin/vim
配置Vundle
git clone https://github.com/VundleVim/Vundle.vim.git ~/.vim/bundle/Vundle.vim
vi ~/.vimrc
输入
：
set nocompatible " be iMproved, required
filetype off " required
" set the runtime path to include Vundle and initialize
set rtp+=~/.vim/bundle/Vundle.vim
call vundle#begin()
" alternatively, pass a path where Vundle should install plugins
"call vundle#begin('~/some/path/here')
Plugin 'scrooloose/nerdtree'
Plugin 'majutsushi/tagbar'
Plugin 'kien/ctrlp.vim'
Plugin 'powerline/powerline'
" let Vundle manage Vundle, required
Plugin 'VundleVim/Vundle.vim'
" The following are examples of different formats supported.
" Keep Plugin commands between vundle#begin/end.
" plugin on GitHub repo
Plugin 'tpope/vim-fugitive'
" plugin from http://vim-scripts.org/vim/scripts.html
" Plugin 'L9'
" Git plugin not hosted on GitHub
" Plugin 'git://git.wincent.com/command-t.git'
" git repos on your local machine (i.e. when working on your own plugin)
" Plugin 'file:///home/gmarik/path/to/plugin'
" The sparkup vim script is in a subdirectory of this repo called vim.
" Pass the path to set the runtimepath properly.
Plugin 'rstacruz/sparkup', {'rtp': 'vim/'}
" Install L9 and avoid a Naming conflict if you've already installed a
" different version somewhere else.
" Plugin 'ascenator/L9', {'name': 'newL9'}
" Solarized: 非常流行的配色。
Plugin 'altercation/vim-colors-solarized'
" Commentary: 快速注释。
Plugin 'tpope/vim-commentary'
" Airline: 小巧美观的状态栏。
" Plugin 'bling/vim-airline'
Plugin 'Valloric/YouCompleteMe'
" for VCM
let g:ycm_global_ycm_extra_conf = '~/.ycm_extra_conf.py'
"let g:ycm_key_invoke_completion = '<C-j>'
"let g:ycm_semantic_triggers = {}
"let g:ycm_semantic_triggers.c = ['->', '.', ' ', '(', '[', '&']
let g:ycm_confirm_extra_conf=1
nnoremap <C-g> :YcmCompleter GoToDefinitionElseDeclaration<CR>
" All of your Plugins must be added before the following line
call vundle#end() " required
filetype plugin indent on " required
" To ignore plugin indent changes, instead use:
"filetype plugin on
"
" Brief help
" :PluginList - lists configured plugins
" :PluginInstall - installs plugins; append `!` to update or just :PluginUpdate
" :PluginSearch foo - searches for foo; append `!` to refresh local cache
" :PluginClean - confirms removal of unused plugins; append `!` to auto-approve removal
"
" see :h vundle for more details or wiki for FAQ
" Put your non-Plugin stuff after this line
进入VIM安装Plugin：
vim
:PluginInstall
安装YCM：
cd ~/.vim/bundle/YouCompleteMe
./install.py --clang-completer #这一步可能要等很久，下载clang好慢
安装完成后发现还是不能用，YCM没有任何提示。
在vim中查看log：
:YcmToggleLogs ycmd_43693_stderr_EstRnF.log
发现提示：“version `GLIBCXX_3.4.20’ not found”
使用：
strings /usr/lib/x86_64-linux-gnu/libstdc++.so.6 | grep GLIBCXX
发现最高只有GLIBCXX_3.4.19
上面升级GCC到4.9.2的时候，只把bin文件的东西考过去，并没有把新的libstdc++.so.6也搞过来。
接下去执行
locate libstdc++.so
得到结果：
把opt下libstdc++.so.6.0.20拷贝到/usr/lib/x86_64-linux-gnu/下， 并制作软连接：
sudo cp /opt/gcc-4.9.2/lib64/libstdc++.so.6.0.20 /usr/lib/x86_64-linux-gnu/
sudo rm /usr/lib/x86_64-linux-gnu/libstdc++.so.6
sudo ln -s /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.20 /usr/lib/x86_64-linux-gnu/libstdc++.so.6
再次使用VIM就可以看到好用的YCM啦！