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字符串的比较，用 a compare:b 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");      }

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");      }

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 = YES     */｝

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 = YES */}

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 = 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

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