iOS版本比较方法

之前一直把版本号转换为floatValue,但是最近在项目中又出现了float的问题，主要是

NSString表示为@"17.30",转换为floatValue 值为17.299999,然后做了一些放大处理，导致不精确，就是精度少了1

所以都不敢在系统版本比较的过程中把值强制转换为floatValue了。

/* * System Versioning Preprocessor Macros */ #define SYSTEM_VERSION_EQUAL_TO(v)([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch]==NSOrderedSame) #define SYSTEM_VERSION_GREATER_THAN(v)([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch]==NSOrderedDescending) #define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch]!=NSOrderedAscending) #define SYSTEM_VERSION_LESS_THAN(v)([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch]==NSOrderedAscending) #define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v)([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch]!=NSOrderedDescending) /* * Usage */if(SYSTEM_VERSION_LESS_THAN(@"4.0")){...} if(SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"3.1.1")){...}