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

个人系统是Debian 9.8， 而后在装下面这两个包的时候总是提示找不到。而后再github上一问，过了几分钟就有大佬回复了，并且亲测有效

~$ 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'

要解决这个问题，首先你得修改/etc/apt/source.list文件（也有多是source.conf文件），在最后加上下面这行命令

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

而后更新库

sudo apt-get update
sudo apt-get upgrade

最后从新运行安装命令便可

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