title: VS2022 preview, error C7612: could not find header unit for…” on importing a standard header (for example “import <vector>;”
body: <p>From my limited understanding the following should compile,</p>
  <pre><code>import &lt;concepts&gt;;
  </code></pre>
  <p>I found the following related bug on MS Developer Community with the comment,</p>
  <p>[severity:It bothers me. A fix would be nice]
  I’m getting “error C7612: could not find header unit for…” on importing a standard header (for example “import ;” ) in any cpp-file whenever there is no correspondig import in an ixx-file. There is no step for vector in “1&gt;Scanning sources for module dependencies…” unless it is mentioned in an ixx-file.</p>
  <p>I could not identify the bug, and it is closed as not a bug. This seems to be pertaining to an earlier compiler. I'm using VS2022 preview.</p>
  <p>I tried to work with the advanced compiler options on VS2022 as suggested by Olga and I could not find a way to use the import directive for a standard header file.</p>
  <p>The current header units support is more like precompiled headers support and require some user action to tell project system which header units to build. Please refer to Project System section in <a href="https://devblogs.microsoft.com/cppblog/standard-c20-modules-support-with-msvc-in-visual-studio-2019-version-16-8/" rel="nofollow noreferrer">https://devblogs.microsoft.com/cppblog/standard-c20-modules-support-with-msvc-in-visual-studio-2019-version-16-8/</a> for the recommended way of doing this.</p>
  <p>You can also set “Scan All Sources for Module Dependencies” to “Yes” in C/C++ Advanced page of Project (of File) Properties UI.
  It will make project system automatically build all imports. but will build and intellisense will be slower.</p>
  <p>The reason I am jumping to this as this is an incredibly important feature I have been waiting on and I need to see it work so I could be reasonably confident with forward development using the mechanism. This also fails on GCC.</p>
  <p>Now I understand that it requires great compiler tool support. It reminds me of having to compile boost, this is going back some time. There seems to be a flavor of PCH involved with this too.</p>
  <p>I hope there is a simple way in order to support importing of standard header files.</p>
  <p>Emily</p>