IOS编译时有时出现这样的错误，要注意，错误不在Undefined for architecture i386，而是下面下划线开头的变量没定义，此时需要导入libz到项目即可。
Undefined symbols for architecture i386: "_crc32", referenced from:
原文：http://www.cnblogs.com/dzut/p/4265017.html
