29. The TYPEDEF Operator

• The TYPEDEF operator creates a user-defined type.

• A user-defined type has the status of a built-in type when defining variables.

• TYPEDEF is ideal for creating pointer variables.

• For example, PBYTE and PWORD are pointers to bytes and words, respectively:

      PBYTE TYPEDEF PTR BYTE
      PWORD TYPEDEF PTR WORD
  
      .DATA               ; Begin data segment
          b_array     BYTE    0, 1, 2, 4, 8
          w_array     WORD    1000h, 2000h, 3000h
          ptr_b_arr   PBYTE   OFFSET b_array
          ptr_w_arr   PWORD   OFFSET w_array
  
      .CODE               ; Begin code segment
  
          mov esi, ptr_b_arr
          inc esi
          inc esi
          mov al, [esi]   ; AL <- 2
          
          mov esi, ptr_w_arr
          add esi, TYPE w_array
          mov ax, [esi]   ; AX <- 2000h