title: C preprocessor: stringize macro and identity macro
body: <p>I want to know the reason behind the output of this code. I couldn't come up with an answer.</p>
  
  <pre><code>#define f(a,b) a##b
  #define g(a) #a
  #define h(a) g(a)
  void main()
  {
     printf("%s %s",h(f(1,2)),g(f(1,2)));
  }
  </code></pre>
  
  <p>PS: output is <code>12 f(1,2)</code>. I thought it was <code>12 12</code> or <code>f(1,2) f(1,2)</code>.</p>