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是否可以看到一个字符串以数字结尾,而该数字的长度未知?检查NSString的最后一个字符是否为数字
- “字符串1” - > 1
- “字符串4356” - > 4356
- “字符串” - >零
如果是这样,我怎么能确定这个数字?
是否可以看到一个字符串以数字结尾,而该数字的长度未知?检查NSString的最后一个字符是否为数字
如果是这样,我怎么能确定这个数字?
要测试一个字符串结尾的数字,你可以使用一个NSPredicate,如:
NSPredicate endsNumerically = [NSPredicate predicateWithFormat:@"SELF matches %@", @"\\d+$"];
[endsNumerically evaluateWithObject:string]; // returns TRUE if predicate succeeds
NSScanner
有时是从字符串中提取有用的东西,但它不向后扫描。您可以定义一个Gnirts(反向字符串)类并将其用于NSScanner,但这可能比它的价值更麻烦。
的NSString的rangeOfCharacterFromSet:options:
,我曾希望用,只查找单个字符(它像strchr
and strrchr
,如果你熟悉C),但我们可以推出我们自己从一组返回字符的连续范围(有点像strspn
)作为NSString
上的category。当我们处理它时,让我们包含返回子字符串而不是范围的方法。
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
要使用新的类别检查一个字符串的数字结束或提取号码:
NSString* number = [string substringFromSet:[NSCharacterSet decimalDigitCharacterSet]
options:NSBackwardsSearch|NSAnchoredSearch];
if (number != nil) {
return [number intValue];
} else {
// string doesn't end with a number.
}
最后,您可以使用第三方正则表达式库,如RegexKit或RegexkitLite。
感谢您的回复。我认为您的第二个片段中有两个拼写错误。范围应该是digitRange,==应该是!=正确的?另外,第二个片段找到值为12的2。我想找到所有正数,而不是关于它们的密码量。这也可能与您的第二个片段,或者我应该去的正则表达式库? – 2010-04-03 11:59:29
@迈克尔:是的。本来,我有“字符串不以数字结尾”分支,显然,我忽略了对测试的反转。我会用一个片段更新我的答案,一旦我休息一下,就会提取整个数字。 – outis 2010-04-03 13:14:42
感谢您为我检查出来。 – 2010-04-03 14:04:16