5

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 给我上面定义的过程 foo 的以下错误:

来自实例的预期类型“System.Address_To_Access_Conversions.Object_Pointer”...
发现类型“Node_Ptr”定义在...

Object_Pointer 定义为访问所有对象。据我了解,Object 类型是 Node,因此 Object_Ptr 可以访问所有 Node。蚊子在抱怨什么?
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:我用“gnatmake -gnatG”编译了我的代码以查看通用实例化:

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 是上面定义的类型 Node 的重命名,所以我真的认为 to_address() 的参数类型是正确的,但是 gnat 抱怨(见上文)。

4

2 回答 2

5

目前我面前没有编译器,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; 
于 2010-05-06T20:37:05.377 回答
1

好的,显式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;

需要一些时间来适应 Ada... ;-)

于 2010-05-06T18:36:40.663 回答