_gzwrite _gzclose referenced from - symbol(s) not found

If you are suffering from this build error
just add framework "libz.dylib" to your iPhone project.

It's a "link" error.
For problems like "xxxx reference from ... symbol(s) not found", try to find the missing framework.

Search the link-error method, and "Jump to Definition", you would probably see what framework it is referencing from.