title: error when import zlib in iOS: symbol(s) not found collect2: ld
body: <p>I have included <code>&lt;zlib.h&gt;</code> in my iphone application and the source code I was mocking up the sample code of Molecules provided by Brad Larson, however, when I build the project, it returns the error as below.  Can anyone point out for me whether this is a library linking problem or am I missing something else?</p>
  
  <pre><code>"_deflate", referenced from: -[NSData(Gzip) gzipDeflate] in NSData+Gzip.o "_inflateEnd", 
  referenced from: -[NSData(Gzip) initWithGzippedData:] in NSData+Gzip.o "inflateInit2", 
  referenced from: -[NSData(Gzip) initWithGzippedData:] in NSData+Gzip.o "_inflate", 
  referenced from: -[NSData(Gzip) initWithGzippedData:] in NSData+Gzip.o "_deflateEnd", 
  referenced from: -[NSData(Gzip) gzipDeflate] in NSData+Gzip.o "deflateInit2", referenced 
  from: -[NSData(Gzip) gzipDeflate] in NSData+Gzip.o ld: symbol(s) not found collect2: ld 
  returned 1 exit status
  </code></pre>