NSOrderedSame NSOrderedAscending NSOrderedDescending枚举比较a==b

 NSString 两个字符串的比较，用 a compare:b 来比，得出的结果分3种  

1. 26个字母比较  越靠后面  越大
    NSString *a = @"qweqwe";
    NSString *b = @"qweasd";
    BOOL result = [a compare:b];
    if (result == NSOrderedSame) {          // NSOrderedSame = 0 完全一样
        NSLog(@"a = b");
    }else if(result == NSOrderedAscending)  // NSOrderedAscending = -1
        NSLog(@"a < b");
    else{                                   //NSOrderedDescending = +1
        NSLog(@"a > b");
    }
 
    2011-07-05 15:04:33.951 Q[5180:207] a > b

2.比较数字或者符号，或者字母 什么都行
 
   NSString *a = @"1.0.30qweqwe";
    NSString *b = @"1.0.45qweasd";
    BOOL result = [a compare:b];
    if (result == NSOrderedSame) {          // NSOrderedSame = 0 完全一样
        NSLog(@"a = b");
    }else if(result == NSOrderedAscending)  // NSOrderedAscending = -1
        NSLog(@"a < b");
    else{                                   //NSOrderedDescending = +1
        NSLog(@"a > b");
    }
 
  2011-07-05 15:05:13.175 Q[5209:207] a < b

3.不考虑大小写比较字符串 
[a caseInsensitiveCompare:b]
 
 
 
- (void)viewDidLoad
{
    NSString *a = @"i love my boyfriend.";
    NSString *b = @"I Love My Boyfriend.";
    NSLog(@" \n a:  %@ \n",a);
    NSLog(@" \n b:  %@ \n",a);
    BOOL result = [a caseInsensitiveCompare:b] ==  NSOrderedSame;
｝
// result = (BOOL) YES;

4.不考虑大小写比较字符串 
[a caseInsensitiveCompare:b]
 
- (void)viewDidLoad
{
    NSString *a = @"i love my boyfriend.";
    NSString *b = @"Little baby.";
    NSLog(@" \n a:  %@ \n",a);
    NSLog(@" \n b:  %@ \n",a);
    BOOL result = [a caseInsensitiveCompare:b] ==  NSOrderedAscending;
}
//result = (BOOL) YES;


5. 有选择的比较大小   [a compare:b options:NSCaseInsensitiveSearch|NSNumericSearch]
- (void)viewDidLoad
{
    NSString *a = @"i love my boyfriend.";
    NSString *b = @"I Love My Boyfriend.";
    NSLog(@" \n a:  %@ \n",a);
    NSLog(@" \n b:  %@ \n",b);
    BOOL result = [a compare:b options:NSCaseInsensitiveSearch|NSNumericSearch] ==  NSOrderedSame;
}
//result = (BOOL)YES;
NSCaseInsensitiveSearch  忽略大小写的比较字符串
NSNumericSearch       比较字符串的个数
NSLiteralSearch       区分大小写，进行完全比较