iOS动态库

经常有某些第三方类库需要添加libz.dylib文件，不知道其作用。同时libz貌似有很多版本，什么1.2.5，1.1.3什么的，各版本之间有啥差异呢？

A file ending in the extension .dylib is a dynamic library: it's a library that's loaded at runtime instead of at compile time. If you're familiar with DLLs from Windows or DSOs, it's more or less the same type of thing with a few twists. The Dynamic Library Programming Topics section of the Mac OS X Developer Library covers all the details about the format and what you should be aware of.

libz.dylib is the dynamic library for Zlib, a general compression library. PDFs can (and usually do) use zlib to compress different aspects of the data contained within them, but accessing the PDF data at that level is pretty low-level, and higher-level libraries would abstract most of that type of stuff.

dylib反编译：

dylib是mac os或者iphone os上的动态连接库文件，因为里面很多机器代码，除非你牛XXXX，不然没法改动的。可用otool查文件头的信息啊，用IDA对dylib进行反汇编，找到你要修改的十六进制代码，之后再用十六进制代码查看器UltraEdit修改。