Pascal 指针指向指针

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  指针指向指针

  指向指针的指针是多种间接形式或一系列指针。通常，指针包含变量的地址。当我们定义指向指针的指针时，第一个指针包含第二个指针的地址，该地址指向包含实际值的位置，如下所示。

  

  指向指针的变量必须这样声明。例如，

  
  type
     iptr = ^integer;
     pointerptr = ^ iptr;
  

  以下示例将说明概念并显示地址-

  
  program exPointertoPointers;
  type
     iptr = ^integer;
     pointerptr = ^ iptr;
  
  var
     num: integer;
     ptr: iptr;
     pptr: pointerptr;
     x, y : ^word;
  
  begin
     num := 3000;
     
     (* take the address of var *)
     ptr := @num;
     
     (* take the address of ptr using address of operator @ *)
     pptr := @ptr;
     
     (* let us see the value and the adresses *)
     x:= addr(ptr);
     y := addr(pptr);
     
     writeln('Value of num = ', num );
     writeln('Value available at ptr^ = ', ptr^ );
     writeln('Value available at pptr^^ = ', pptr^^);
     writeln('Address at ptr = ', x^); 
     writeln('Address at pptr = ', y^);
  end. 
  

  尝试一下

  编译并执行上述代码后，将产生以下结果-

  
  Value of num = 3000
  Value available at ptr^ = 3000
  Value available at pptr^^ = 3000
  Address at ptr = 50960
  Address at pptr = 50976