title: In Protocol Buffers, how to import a file from the upper level directory?
body: <p>I have the following code in a protocol buffer file(pcfg_lm.proto):</p>
  
  <pre><code>import "../types/language.proto";
  
  package nlp;
  
  message PCFGProto {
    required Language lang = 1;
  }
  </code></pre>
  
  <p>And of course there is a proto file exists at ../types/language.proto. However, when I issue the command:</p>
  
  <pre><code>protoc pcfg_lm.proto --cpp_out=/tmp
  </code></pre>
  
  <p>Here is the error message:</p>
  
  <pre><code>../types/language.proto: File not found.
  pcfg_lm.proto: Import "../types/language.proto" was not found or had errors.
  pcfg_lm.proto:6:12: "Language" is not defined.
  </code></pre>
  
  <p>I think there must be some way to specify the file names in the upper level directories, without using the -I flag. But how do I do that?</p>