檢查NSString的最後一個字符是否爲數字

Question

是否可以看到一個字符串以數字結尾，而該數字的長度未知？

1. 「字符串1」 - > 1
2. 「字符串4356」 - > 4356
3. 「字符串」 - >零

如果是這樣，我怎麼能確定這個數字？

Answer 1

要測試一個字符串結尾的數字，你可以使用一個NSPredicate，如：

NSPredicate endsNumerically = [NSPredicate predicateWithFormat:@"SELF matches %@", @"\\d+$"]; 
[endsNumerically evaluateWithObject:string]; // returns TRUE if predicate succeeds 

NSScanner有時是從字符串中提取有用的東西，但它不向後掃描。您可以定義一個Gnirts（反向字符串）類並將其用於NSScanner，但這可能比它的價值更麻煩。

的NSString的rangeOfCharacterFromSet:options:，我曾希望用，只查找單個字符（它像strchr and strrchr，如果你熟悉C），但我們可以推出我們自己從一組返回字符的連續範圍（有點像strspn）作爲NSString上的category。當我們處理它時，讓我們包含返回子字符串而不是範圍的方法。

RangeOfCharacters.h：

@interface NSString (RangeOfCharacters) 
/* note "Characters" is plural in the methods. It has poor readability, hard to 
* distinguish from the rangeOfCharacterFromSet: methods, but it's standard Apple 
* convention. 
*/ 
-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet; 
-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask; 
-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask range:(NSRange)range; 

// like the above, but return a string rather than a range 
-(NSString*)substringFromSet:(NSCharacterSet*)aSet; 
-(NSString*)substringFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask; 
-(NSString*)substringFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask range:(NSRange)range; 
@end 

RangeOfCharacters.m：

@implementation NSString (RangeOfCharacters) 
-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet { 
    return [self rangeOfCharactersFromSet:aSet options:0]; 
} 

-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask { 
    NSRange range = {0,[self length]}; 
    return [self rangeOfCharactersFromSet:aSet options:mask range:range]; 
} 

-(NSRange)rangeOfCharactersFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask range:(NSRange)range { 
    NSInteger start, curr, end, step=1; 
    if (mask & NSBackwardsSearch) { 
     step = -1; 
     start = range.location + range.length - 1; 
     end = range.location-1; 
    } else { 
     start = range.location; 
     end = start + range.length; 
    } 
    if (!(mask & NSAnchoredSearch)) { 
     // find first character in set 
     for (;start != end; start += step) { 
      if ([aSet characterIsMember:[self characterAtIndex:start]]) { 
#ifdef NOGOTO 
       break; 
#else 
       // Yeah, a goto. If you don't like them, define NOGOTO. 
       // Method will work the same, it will just make unneeded 
       // test whether character at start is in aSet 
       goto FoundMember; 
#endif 
      } 
     } 
#ifndef NOGOTO 
     goto NoSuchMember; 
#endif 
    } 
    if (![aSet characterIsMember:[self characterAtIndex:start]]) { 
    NoSuchMember: 
     // no characters found within given range 
     range.location = NSNotFound; 
     range.length = 0; 
     return range; 
    } 

FoundMember: 
    for (curr = start; curr != end; curr += step) { 
     if (![aSet characterIsMember:[self characterAtIndex:curr]]) { 
      break; 
     } 
    } 
    if (curr < start) { 
     // search was backwards 
     range.location = curr+1; 
     range.length = start - curr; 
    } else { 
     range.location = start; 
     range.length = curr - start; 
    } 
    return range; 
} 

-(NSString*)substringFromSet:(NSCharacterSet*)aSet { 
    return [self substringFromSet:aSet options:0]; 
} 

-(NSString*)substringFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask { 
    NSRange range = {0,[self length]}; 
    return [self substringFromSet:aSet options:mask range:range]; 
} 
-(NSString*)substringFromSet:(NSCharacterSet*)aSet options:(NSStringCompareOptions)mask range:(NSRange)range { 
    NSRange range = [self rangeOfCharactersFromSet:aSet options:mask range:range]; 
    if (NSNotFound == range.location) { 
     return nil; 
    } 
    return [self substringWithRange:range]; 
} 
@end 

要使用新的類別檢查一個字符串的數字結束或提取號碼：

NSString* number = [string substringFromSet:[NSCharacterSet decimalDigitCharacterSet] 
          options:NSBackwardsSearch|NSAnchoredSearch]; 
if (number != nil) { 
    return [number intValue]; 
} else { 
    // string doesn't end with a number. 
} 

最後，您可以使用第三方正則表達式庫，如RegexKit或RegexkitLite。