title: How to install a Rust target for a specific rustup toolchain?
body: <p>I am using <code>rustc</code> and <code>cargo</code> on my 64-bit Windows machine to compile a 32-bit application. This work fine when using the stable toolchain, but when I try to use the beta toolchain it fails.</p>
  
  <p>The beta toolchain was successfully installed with <code>rustup install beta</code>. In the project folder there is a <code>.cargo/config</code> file containing the following lines:</p>
  
  <pre><code>[build]
  target = "i686-pc-windows-msvc"
  
  [target.i686-pc-windows-msvc]
  rustflags = ["-Ctarget-feature=+crt-static"]
  </code></pre>
  
  <p>When running <code>cargo +beta build</code> the following error occurs:</p>
  
  <pre class="lang-none prettyprint-override"><code>error[E0463]: can't find crate for `core`
    |
    = note: the `i686-pc-windows-msvc` target may not be installed
  </code></pre>
  
  <p>I have tried running <code>rustup target add i686-pc-windows-msvc</code> to fix the issue but it didn't help; <code>rustup target list</code> even displays it as "installed". Possibly this command only adds the target for stable, and I couldn't find out how to specify the beta toolchain.</p>
  
  <p>How can I add another (non-default) target for the beta toolchain?</p>