Question

I’m looking for an Objective-C way of sorting characters in a string, as per the answer to this question.

Ideally a function that takes an NSString and returns the sorted equivalent.

Additionally I’d like to run length encode sequences of 3 or more repeats. So, for example ‘mississippi’ first becomes ‘iiiimppssss’, and then could be shortened by encoding as ‘4impp4s’.

I’m not expert in Objective-C (more Java and C++ background) so I’d also like some clue as to what is the best practice for dealing with the memory management (retain counts etc – no GC on the iphone) for the return value of such a function. My source string is in an iPhone search bar control and so is an NSString *.

Answer 1

int char_compare(const char* a, const char* b) {     if(*a < *b) {         return -1;     } else if(*a > *b) {         return 1;     } else {         return 0;     } }  NSString *sort_str(NSString *unsorted) {     int len = [unsorted length] + 1;     char *cstr = malloc(len);     [unsorted getCString:cstr maxLength:len encoding:NSISOLatin1StringEncoding];     qsort(cstr, len - 1, sizeof(char), char_compare);     NSString *sorted = [NSString stringWithCString:cstr encoding:NSISOLatin1StringEncoding];     free(cstr);     return sorted; } 

The return value is autoreleased so if you want to hold on to it in the caller you’ll need to retain it. Not Unicode safe.