title: What is __CxxFrameHandler4 and what does linker error "unresolved external symbol __CxxFrameHandler4" mean, exactly?
body: <p>I'm using several libraries built through vcpkg (such as civet-web and prometheus-cpp), against my Visual C++ projects. When building x86 all is perfect, in x64 I get a bunch of linker errors:</p>
  <blockquote>
  <p>error LNK2001: unresolved external symbol __CxxFrameHandler4</p>
  </blockquote>
  <p>Searching online all references to this symbol/error are about specific projects, I cannot find what __CxxFrameHandler4 <em>is</em> and what problem this error is highlighting. I don't know if it's a problem with the way vcpkg is building the library, or a problem in my project or how to start looking for a solution.</p>
  <p>I did find this blog article but it is in reference to a preview of VS2019, I cannot find any settings related to it: <a href="https://devblogs.microsoft.com/cppblog/making-cpp-exception-handling-smaller-x64/" rel="noreferrer">https://devblogs.microsoft.com/cppblog/making-cpp-exception-handling-smaller-x64/</a></p>
  <p>If anyone can explain what this is all about it would be a big help.</p>