iOS -- NSString 轉 C string and vise versa

// 從 NSString 轉成 char (C 語言物件：C string）:

   NSString *aStr = @"Hello CQ!";
   const char *update = [aStr cStringUsingEncoding:NSUTF8StringEncoding];
   printf("%s\n",  update);

或是：

e.g. 1
const char *ptr2 = [aStr UTF8String];
printf("%s\n", ptr2);



e.g. 2 (適用在建立 sqlite3 的query)

NSString *query = [NSString stringWithFormat:@"SELECT %@ FROM %@ WHERE %@ = %@ ORDER BY %@, destinationColumn, aTablename, aColumn, aString, ROWID";
    const char * sql = [query UTF8String];


********************************

// C string 轉  NSString

ptr = "C string to string object";
NSString *str = [NSString stringWithCString:ptr encoding:NSUTF8StringEncoding];
NSLog(@"%@", str);