NSString 常用方法

//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;

---