title: what happens if an #include fails to find file
body: <p>Say I have this very basic c++ code:</p>
  
  <p>myCode.cpp:</p>
  
  <pre><code>#include &lt;library1.h&gt;
  #include &lt;library2.h&gt;
  
  int main() {
   // use some methods from library2
  }
  </code></pre>
  
  <p>What will happen if I compile this code but my compiler can't find library1.h? Will it throw any specific error? Will it still look for library2.h? Will it skip the rest of the #include statements and go on to compiling main? I'm asking because I'm trying to answer <a href="https://stackoverflow.com/questions/17001780/linker-error-using-opencv-with-fftw3-visual-studio-2010">this SO question</a> where adding one .h file is causing the compiler to complain about not finding methods from another .h file . Without the #include first .h line, the code compiles correctly.</p>