在iOS的实际开发中，常会出现需要去除空格的情况，总结有三种情况：

• 去除字符串首尾连续字符（如空格）；
• 去除字符串首部连续字符（如空格）；
• 去除字符串尾部连续字符（如空格）；

去除字符串首尾连续字符（如空格）

 NSString *a = @" a  sdf  ";
 [a stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

去除字符串首部连续字符（如空格）；

 NSString *a = @" a  sdf  ";  
 NSString *leftResult = [a stringByTrimmingLeftCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

#import "NSString+util.h"

@implementation NSString (util)

- (NSString *)stringByTrimmingLeftCharactersInSet:(NSCharacterSet *)characterSet {
    NSUInteger location = 0;
    NSUInteger length = [self length];
    unichar charBuffer[length];
    [self getCharacters:charBuffer range:NSMakeRange(0, length)];
    
    for (NSInteger i = 0; i < length; i++) {
        if (![characterSet characterIsMember:charBuffer[i]]) {
            location = i;
            break;
        }
    }
    
    return [self substringWithRange:NSMakeRange(location, length - location)];
}

去除字符串尾部连续字符（如空格）；

NSString *a = @" a  sdf  "; 
NSString *rightResult = [a stringByTrimmingRightCharactersInSet:[NSCharacterSet whitespaceCharacterSet]]; 

- (NSString *)stringByTrimmingRightCharactersInSet:(NSCharacterSet *)characterSet {
    NSUInteger length = [self length];
    unichar charBuffer[length];
    [self getCharacters:charBuffer range:NSMakeRange(0, length)];
    
    NSUInteger subLength = 0;
    for (NSInteger i = length; i > 0; i--) {
        if (![characterSet characterIsMember:charBuffer[i - 1]]) {
            subLength = i;
            break;
        }
    }
    
    return [self substringWithRange:NSMakeRange(0, subLength)];
}