//是否以str开头
- (BOOL)hasPrefix:(NSString*)str;
//是否以str结束
- (BOOL)hasSuffix:(NSString*)str;
//是否包含某字符串
- (NSRange)rangeOfString:(NSString*)searchString;
//是否包含某字符串(副加查找条件)
- (NSRange)rangeOfString:(NSString*)searchString options:(NSStringCompareOptions)mask;
typedefNS_OPTIONS(NSUInteger, NSStringCompareOptions)
{
NSCaseInsensitiveSearch = 1,//不区分大小写比较
NSLiteralSearch = 2,//逐字节比较区分大小写
NSBackwardsSearch = 4,//从字符串末尾开始搜索
NSAnchoredSearch = 8,//搜索限制范围的字符串
NSNumericSearch = 64,//按照字符串里的数字为依据，算出顺序。例如 Foo2.txt < Foo7.txt < Foo25.txt
NSDiacriticInsensitiveSearchNS_ENUM_AVAILABLE(10_5, 2_0) = 128,//忽略 "-" 符号的比较
NSWidthInsensitiveSearchNS_ENUM_AVAILABLE(10_5, 2_0) = 256,//忽略字符串的长度，比较出结果
NSForcedOrderingSearchNS_ENUM_AVAILABLE(10_5, 2_0) = 512,//忽略不区分大小写比较的选项，并强制返回 NSOrderedAscending 或者 NSOrderedDescending
NSRegularExpressionSearchNS_ENUM_AVAILABLE(10_7, 3_2) = 1024//只能应用于 rangeOfString:..., stringByReplacingOccurrencesOfString:...和 replaceOccurrencesOfString:... 方法。使用通用兼容的比较方法，如果设置此项，可以去掉 NSCaseInsensitiveSearch 和 NSAnchoredSearch
};
//替换字符串
- (NSString*)stringByReplacingOccurrencesOfString:(NSString*)target withString:(NSString*)replacement;
//某一位置上的字符
- (unichar)characterAtIndex:(NSUInteger)index;
