The right way to reverse a string

NSString+Reverse.m

#import <Foundation/Foundation.h>

void strrev(char *str) {
    size_t start = 0;
    size_t end = start + strlen(str) - 1;
    
    while (start < end) {
        char ch = str[start];
        str[start++] = str[end];
        str[end--] = ch;
    }
}

void strrev2(char *str) {
    size_t len = mbstowcs(NULL, str, 0);
    wchar_t *wcs = (wchar_t *) calloc(len + 1, sizeof(wchar_t));
    
    mbstowcs(wcs, str, len + 1);
    
    size_t start = 0;
    size_t end = start + len - 1;
    
    while (start < end) {
        wchar_t wc = wcs[start];
        wcs[start++] = wcs[end];
        wcs[end--] = wc;
    }
    
    wcstombs(str, wcs, wcstombs(NULL, wcs, 0));
    free(wcs);
}

@implementation NSString (Reverse)

- (NSString *)my_stringByReversing {
    NSUInteger length = [self lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
    char *str = (char *) calloc(1, length);
    [self getBytes:str
         maxLength:length
        usedLength:nil
          encoding:NSUTF8StringEncoding
           options:0
             range:NSMakeRange(0, self.length)
    remainingRange:nil];
    
    strrev2(str);
    NSString *reversed = [NSString stringWithCString:str encoding:NSUTF8StringEncoding];
    free(str);
    
    return reversed;
}

@end