E: Unable to locate package clang-7 E: Unable to locate package clang++-7 E: Couldn't find any packa

個人系統是Debian 9.8， 而後在裝下面這兩個包的時候總是提示找不到。而後再github上一問，過了幾分鐘就有大佬回覆了，並且親測有效

~$ sudo apt-get -y install clang-7 clang++-7
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package clang-7
E: Unable to locate package clang++-7
E: Couldn't find any package by regex 'clang++-7'

要解決這個問題，首先你得修改/etc/apt/source.list文件（也有多是source.conf文件），在最後加上下面這行命令

deb http://deb.debian.org/debian/ testing main

而後更新庫

sudo apt-get update
sudo apt-get upgrade

最後從新運行安裝命令便可

~$ sudo apt-get -y install clang-7 clang++-7