[Solved]missing config key `build.target`

$ cargo -v build
error: missing config key `build.target`
$ rustup show
Default host: x86_64-pc-windows-msvc
rustup home:  E:\rustup

installed toolchains
--------------------

nightly-i686-pc-windows-msvc
nightly-x86_64-pc-windows-msvc (default)

active toolchain
----------------

nightly-x86_64-pc-windows-msvc (default)
rustc 1.41.0-nightly (3eeb8d4f2 2019-12-12)

I had uninstalled rustup by accident.But, after reinstalling it.I got this error and I can't figure out what's wrong.

I would consider completely reinstalling rust, I had a problem much like this, and reinstalling fixed it.