Using CFEqual with CFArray and CFDictionary

Question

I have NSArray that contains NSDictionaries. I need to convert it to CFMutableArray that contains items of type CFMutableDictionary with char* keys and values.

- (CFArrayRef)cStringDataSet {
CFArrayCallBacks cfTypeCallBacks = {0, NULL, NULL, NULL, CFEqual};
CFMutableArrayRef cStrDataSet = CFArrayCreateMutable(NULL, 0, &cfTypeCallBacks);

CFDictionaryKeyCallBacks charKeyCallBacks = {0, NULL, NULL, NULL, charEqual, charHash};
CFDictionaryValueCallBacks charValueCallBacks = {0, NULL, NULL, NULL, charEqual};

for (NSDictionary *dict in dataSet) {
    CFMutableDictionaryRef cStrDict = CFDictionaryCreateMutable(NULL, 0, &charKeyCallBacks, &charValueCallBacks);

    for (NSString *key in [dict allKeys]) {
        const char *cStrKey = [key UTF8String];
        const char *cStrValue = [[[dict objectForKey:key] description] UTF8String];

        CFDictionaryAddValue(cStrDict, cStrKey, cStrValue);
    }

    CFArrayAppendValue(cStrDataSet, cStrDict);
}

return cStrDataSet;
}

charEqual and charHash are defined as follows:

Boolean charEqual(const void *ptr1, const void *ptr2) {
char *char1 = (char*)ptr1;
char *char2 = (char*)ptr2;

if (strlen(char1) != strlen(char2)) {
    return false;
}

return !strncmp(char1, char2, strlen(char1));
}

CFHashCode charHash(const void *ptr) {
    return (CFHashCode)((int)ptr);
}

Now I want to compare two CFArrayRefs using CFEqual, but function charEqual is never called and CFEqual always returns "false".

Answer 1

You're violating the constraints on equality and hash codes. If two strings compare equal, then they must have the same hash code too. If the dictionary is implemented using buckets, it will first calculate a hash code, and only if it finds a match for that hash code will it call the comparison function.

You need to make sure charEqual(char1, char2) is true only if charHash(char1) == charHash(char2), which means you need to reimplement charHash based on the value of the string, not its address.