在ubuntu22.04中添加安装并设置默认编译器。

1. gcc --version  //查看当前gcc版本

2. sudo apt-get install gcc    //安装默认版本gcc

sudo apt-get install gcc-7 g++-7 //安装gcc7.5

不同的源下载的gcc版本也不一样，ubuntu22.04默认安装gcc11，而且只有这一个版本。所以添加其他源下载对应版本的gcc

deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse

deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse

deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse

3. apt-cache madison gcc  gcc-7 //查看当前源支持的gcc版本

4. sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-7 100

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-11 100

sudo update-alternatives --config gcc   //切换gcc优先级