title: Adding object (.o) files to qtcreator project
body: <p>How does one add third party .o and .h files to a Qt C++ project in QtCreator? I want to add some compiled .o files from John The Ripper to my probject (ignore the non-cross-platformness of that). As a test, a wrote a small C program (outside QtCreator) and linked it against <code>common.o</code> and <code>MD5_std.o</code> and it worked fine; I can just do <code>gcc -o runme common.o MD5_std.o simpleprogram.c</code>, but with QtCreator, nothing seems to work. I keep getting undefined references.</p>
  
  <p>I tried adding this to the .pro file:</p>
  
  <pre><code>LIBS += "$$_PRO_FILE_PWD_/common.o" "$$_PRO_FILE_PWD_/MD5_std.o" 
  </code></pre>
  
  <p>And this:</p>
  
  <pre><code>LIBS += /full/path/to/common.o /full/path/to/MD5_std.o
  </code></pre>
  
  <p>I also tried setting <code>INCLUDEPATH</code> and adding the .o files as 'other files' and 'sources' in the .pro file, but no matter what I do, the calls to the functions in the .o files always result in undefined references.</p>
  
  <p>Additionally, from all the advice I found on the internet (which did work for them, weirdly enough), I didn't find a way to add the .o files to the project in such a way that they are copied to the shadow build directory, and linked from there. I seems wrong to refer to the <code>$$_PRO_FILE_PWD_</code>.</p>
  
  <p>BTW: What I did get to work, is linking a system lib. When I add <code>-lcrypt</code> to <code>LIBS</code> and include <code>unistd.h</code>, I can call the crypt function just fine.</p>