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(请参阅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给出了以下错误:
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:我用“gnatmake -gnatG”编译我的代码来查看泛型实例化:
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) .
2 回答
我现在面前没有编译器,但这不起作用吗?
好的,显式类型转换可以解决问题:
需要一段时间习惯阿达... ;-)