我正在尝试安装 g++ 4.9 或更高版本以便在 Android 上构建 mapbox。说明指出我需要 g++ 4.9 或更高版本。我找到了以下说明，但它们不起作用。
sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt-get update
sudo apt-get install g++-4.9
最后一条命令说：
~ $ sudo apt-get install g++-4.9
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package g++-4.9 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'g++-4.9' has no installation candidate
我还尝试了 Synaptic Package Manager 并得到以下结果：
g++:
Depends: cpp (>=4:4.9-1ubuntu7) but 4:4.8.2-1ubuntu6 is to be installed
Depends: gcc (>=4:4.9-1ubuntu7) but 4:4.8.2-1ubuntu6 is to be installed
Depends: g++-4.9 (>=4.9) but it is not installable
Depends: gcc-4.9 (>=4.9) but it is not installable
如何在我的计算机上获得 g++ 4.9？
谢谢。
