Given a filename, how can I get the Adler32 using Crypto++

Given a "string filename", how can I get the Adler32 checksum using the C++ Crypto++ library. I am a little confused about using their Source and Sink system.

Below I have the skeleton of the code that does MD5, but I can't seem to find any examples or tutorials on the Adler32 usage.

string filename = "/tmp/data.txt"
string file_adler32_digest;
string file_md5_digest;

MD5 hashMD5;

FileSource fs( filename.c_str(), 
              true, 
              new HashFilter( hashMD5, 
              new HexEncoder( new StringSink( file_md5_digest ) ) ) );

/* Confusion begins here */   

//how do I do the adler32 ?

/* Confusion ends here */

cout << file_adler32_digest << endl
     << file_md5_digest << endl;

Good samples and sample code here http://www.cryptopp.com/wiki/Category:Sample for all the Crypto++ (except for the Adler32 stuff I want)

If you follow this http://www.cryptopp.com/wiki/HashFilter, you have to change hashMD5 for hashAdler32, and file_md5_digest for file_adler32_digest

Adler32 hashAdler32;

FileSource( filename.c_str(), 
            true, 
            new HashFilter( hashAdler32, 
            new HexEncoder( new StringSink( file_adler32_digest ) ) ) );

After this file_adler32_digest should contain the desired hash.