NSString 和NSCharacterset的不同之处
An NSString object represents a string of ordered characters (text). An NSCharacterSet object represents a set of characters in no particular order. It is often much quicker to determine whether a character is a member of an NSCharacterSet than an NSString. You can’t use an NSCharacterSet object to hold text, at least not in any sensible way, because it does not maintain any order of characters, its use is primarily for determining whether a character exists in a set of characters.
我们在nsstring的分割，查找等操作中，经常会提供两种函数，参数类型分别为NSString 和NSCharacterset，有什么不同呢？
NSString 是有序字符串
NSCharacterset是无需字符集合，主要用来判断已知字符串是否包含制定字符集，而不可以用来保存字符串。
转自：http://blog.csdn.net/aiyongyyy/article/details/8269546
在ios中 ��可以使用stringByTrimmingCharactersInSet函数过滤字符串中的特殊符号
首先自己定义一个NSCharacterSet, 包含需要去除的特殊符号
NSCharacterSet *set = [NSCharacterSet characterSetWithCharactersInString:@"/@／：；（）¥「」/＂、[]{}#%-*+=_\\|~＜＞$€^•’@#$%^&*()_+’\""];
由于NSString中有全角符号和半角符号, 因此有些符号要包括全角和半角的
然后调用stringByTrimmingCharactersInSet
NSString *trimmedString = [string stringByTrimmingCharactersInSet:set];
trimmedString就是过滤后的字符串
转自：http://www.gelubpa.com/2012/8/10/00702.html
NSCharacterSet
实例应用：
一、过滤字符串开始位置和结束位置的空格
NSString *testString = @"my name is wang tianqiao ";
NSString *cString = [testString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
NSLog(@"cString is %@",cString);
转自：http://blog.sina.com.cn/s/blog_5421851501014xif.html
NSCharacterSet 去除NSString中的空格
去除 username中的空格，tablenewline，nextline
代码如下：（三行代码）
NSCharacterSet *whitespace =[NSCharacterSet whitespaceAndNewlineCharacterSet];
NSString *username = [mUsernameField stringValue];
username =[username stringByTrimmingCharactersInSet:whitespace];
注释：
stringByTrimmingCharactersInSet:
Returns a new string made by removing from both ends of the receiver characters contained in a given characterset.
whitespaceAndNewlineCharacterSet
Returns a character set containing only the whitespace charactersspace (U+0020) and tab (U+0009) and the newline and nextlinecharacters (U+000A–U+000D, U+0085).
另外可以用 whitespaceCharacterSet 替换 whitespaceAndNewlineCharacterSet 区别
newlinenextline
whitespaceCharacterSet
Returns a character set containing only the in-line whitespacecharacters space (U+0020) and tab (U+0009).
NSString *temptext = [messageTextField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
NSString *text = [temptext stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet ]];
第1行是去除2端的空格
第2行是去除回车
转自：http://mikixiyou.iteye.com/blog/1623323
如何去掉String的前后空格或某字符
在objective-c中，如何去掉一个string的前后的空格字符或某个特定字符呢？
如@“ abc 123 ”字符串前后有空格，该如何去掉？
使用nsstring的实例方法stringByTrimmingCharactersInSet：可以解决该问题。
方法如下：
OC代码
[@"abc123" stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]]；
NSString *newString = [oldString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
NSString中该方法说明如下：
stringByTrimmingCharactersInSet:
Returns a new string made by removing from both endsof the receiver characters contained in a given character set.
– (NSString *)stringByTrimmingCharactersInSet:(NSCharacterSet*)set
Parameters
set
A character set containing the characters to removefrom the receiver. set must not be nil.
Return Value
A new string made by removing from both ends of thereceiver characters contained in set. If the receiver is composedentirely of characters from set, the empty string is returned.