Question

我想打印访问变量（指针）的地址以进行调试。

type Node is private;
type Node_Ptr is access Node;

procedure foo(n: in out Node_Ptr) is
    package Address_Node is new System.Address_To_Access_Conversions(Node);
    use Address_Node;
begin
    Put_Line("node at address " & System.Address_Image(To_Address(n)));
end foo;

Address_Image返回地址的字符串表示形式 System.Address_To_Access_Conversions是一个通用包，用于在地址和访问类型之间进行转换（参见ARM 13.7.2），定义如下：

generic
    type Object(<>) is limited private;
package System.Address_To_Access_Conversions is
   -- [...]
   type Object_Pointer is access all Object;
   -- [...]
   function To_Address(Value : Object_Pointer) return Address;
   -- [...]
end System.Address_To_Access_Conversions;

gnat为上面定义的过程foo提供了以下错误：

expected type "System.Address_To_Access_Conversions.Object_Pointer" from instance at line...
found type "Node_Ptr" defined at ...

Object_Pointer被定义为访问所有对象。根据我的理解，Object类型是Node，因此Object_Ptr访问所有Node。什么是gnat抱怨？
我想我对Ada泛型的理解是有缺陷的，我没有正确使用System.Address_To_Access_Conversions。

编辑：我使用“gnatmake -gnatG”编译了我的代码以查看泛型实例化：

package address_node is
    subtype btree__clear__address_node__object__2 is btree__node;
    type btree__clear__address_node__object_pointer__2 is access
        all btree__clear__address_node__object__2;
    function to_address (value :
        btree__clear__address_node__object_pointer__2) return
        system__address;
end address_node;

btree__node是上面定义的Node类型的错位名称，所以我认为to_address（）的参数类型是正确的，但是gnat正在抱怨（见上文）。

Answer 1

我现在面前没有编译器，但这不起作用吗？

procedure foo(n: in out Node_Ptr) is 
begin 
   Put_Line("node at address " & System.Address_Image(n.all'address)); --'
end foo;

Answer 2

好的，明确的类型转换可以解决问题：

procedure Foo(n: in out Node_Ptr) is
    package Address_Node is new System.Address_To_Access_Conversions(Node);
    use Address_Node;
    p : Address_Node.Object_Pointer;
begin
    p := Address_Node.Object_Pointer(n);
    Put_Line("node at address " & System.Address_Image(To_Address(p)));
end Foo;

需要一些时间习惯Ada ...; - ）

如何打印ada访问变量指向的地址？

2 个答案: