字符串中子字符串的出现次数

Question

这是查找子字符串出现次数的可接受方式吗？可以提高效率吗？应该使用什么编码从a NSString到ac字符串？

我不是100%肯定()!=NULL在while语句中,它似乎工作正常,当没有发现任何更多的事件时,它确实打破了while循环.

- (NSUInteger)occurenceOfString:(NSString *)substring {
    const char *substr = [substring cStringUsingEncoding:NSUTF8StringEncoding];
    const char *selfstr = [self cStringUsingEncoding:NSUTF8StringEncoding];
    unsigned long substrlen = strlen(substr);
    NSUInteger count = 0;
    char * ptr;
    while ((ptr = strstr(selfstr, substr)) != NULL && substr != '\0') {
        count++;
        substr += substrlen + *ptr;
    }
    return count;
}

(这是一种类别方法,因此在自己中搜索字符串).

Answer 1

NSUInteger cnt = 0, length = [str length];
NSRange range = NSMakeRange(0, length); 
while(range.location != NSNotFound)
{
  range = [str rangeOfString: @"substr" options:0 range:range];
  if(range.location != NSNotFound)
  {
    range = NSMakeRange(range.location + range.length, length - (range.location + range.length));
    cnt++; 
  }
}