问生成MD5散列的方法的奇怪行为-返回相同的散列结果

EN

+(NSString *) returnMD5HashOfString:(NSString*)aString 
{   
    // Create byte array of unsigned chars
    unsigned char md5Buffer[CC_MD5_DIGEST_LENGTH];

    // Create 16 byte MD5 hash value, store in buffer
    CC_MD5(aString, aString.length, md5Buffer);

    // Convert MD5 value in the buffer to NSString of hex values
    NSMutableString *output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
    for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) 
        [output appendFormat:@"%02x",md5Buffer[i]];

    return output;
}