//导入这个就行了
#import <CommonCrypto/CommonDigest.h>
//没有导包的时候，提示如下: Implicit declaration of function ‘CC_MD5‘ is invalid in C99
CC_MD5( cStr, strlen(cStr),result);
Implicit declaration of function 'CC_MD5' is invalid in C99,布布扣,bubuko.com
Implicit declaration of function 'CC_MD5' is invalid in C99
原文：http://www.cnblogs.com/hw140430/p/3807645.html