title: How to exculde build-in / system function during function analysis by clang libtooling
body: <p>I'm trying to analyze functions by using clang libtooling.
  Here is the source code that I want to analyze:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  
  int main(){
      int a = 100;
      printf("a==%d", a);
  }
  </code></pre>
  
  <p>when I run my tool to get all the function decl in above files, I found there are a lot of build-in / system functions, like:  </p>
  
  <pre><code>decls: 
  _IO_cookie_init
   __underflow
   __uflow
   __overflow
   _IO_getc
   _IO_putc
   _IO_feof
   _IO_ferror
   _IO_peekc_locked
   _IO_flockfile
   _IO_funlockfile
   _IO_ftrylockfile
   _IO_vfscanf
   _IO_vfprintf
   _IO_padn
   _IO_sgetn
   _IO_seekoff
   _IO_seekpos
   _IO_free_backup_area
   remove
   rename
   renameat
   tmpfile
   tmpfile64
   tmpnam
   tmpnam_r
   tempnam
   fclose
   fflush
   fflush_unlocked
   fcloseall
   fopen
  </code></pre>
  
  <p>(I think they are introduced by the header file "stdio.h" )</p>
  
  <p>my question is:
  How can I get rid of all these built-in/system functions from the "stdio.h" file, or other (system) header files?</p>
  
  <p>Thanks in advance!!!</p>