title: How CFFI use the c file in a certain directory?
body: <p>I am learning to call c in python program by CFFI and write c file named 'add.c' as below :</p>
  
  <pre><code>float add(float f1, float f2)
  {
      return f1 + f2;
  }
  </code></pre>
  
  <p>and a python file named 'demo.py' to call add method in 'add.c':</p>
  
  <pre><code>from cffi import FFI
  
  ffi = FFI()
  ffi.cdef("""
     float(float, float);
  """)
  
  C = ffi.verify("""
     #include 'add.c'
   """, libraries=[]
  )
  
  sum = C.add(1.9, 2.3)
  print sum
  </code></pre>
  
  <p>When I run demo.py, I get the error that add.c file cannot be found. Why file add.c cannot be found and how can I to fix it?</p>