从C传递结构到Ada [英] Passing structure from C to Ada

问题描述

我需要在Ada绑定应用程序中将结构从C传递到Ada。因此，我在Ada和C中都声明了结构，以便两个源端都可以解密结构组成。

I need to pass a structure from C to Ada in an Ada binding application. Thus, I have declared the structure in both Ada and C so that both the source sides can decipher the structure composition.

在C中，

typedef struct {
   int Status_Code;
   int Error_Code;
} Edit_Result_Type;

在Ada，

type Edit_Result_Rec_Type is
   record
      Status     : Integer;
      Error_Code : Integer;
   end record;

pragma Convention (Convention => C, 
                   Entity     => Edit_Result_Rec_Type);

for Edit_Result_Rec_Type use
  record
    Status     at 0 range  0 .. 31;
    Error_Code at 0 range 32 .. 63;
  end record;

type Edit_Result_Rec_Type_Ptr is access all Edit_Result_Rec_Type;

当我通过引用将结构从C传递到Ada时，我想知道：

When I am passing the structure from C to Ada through call by reference, I wanted to know:

1. 如果我声明结构的全部访问矢量类型，可以吗（如上所述- Edit_Result_Rec_Type_Ptr ），并将其直接用作Ada函数中的形式参数。例如：

1. Is it ok if I declare an "access all" vector type for the structure (as done above - Edit_Result_Rec_Type_Ptr) in Ada and use it directly as a formal parameter in Ada function. For Eg:

procedure Process_Data (Edit_Result_Ptr : in out Edit_Result_Rec_Type_Ptr) is
begin
   Edit_Result_Ptr.Status     := 1;
   Edit_Result_Ptr.Error_Code := 0;
end Process_Data;

这种方法是否致命？我知道是的，只是想深入了解如何！

Is this approach FATAL? I know it is, just wanted to know "how" in depth!

还有其他（更好）的通过引用传递呼叫的方法吗？我相信我可以将其作为 System.Address参数传递，并在Ada函数内部的本地向量中进行未经检查的转换到 Edit_Result_Rec_Type_Ptr 中成员？这种方法有致命的危险吗？

Any other (better) approaches for passing through call by reference? I believe I can pass it as a "System.Address" parameter and do an "unchecked conversion" into Edit_Result_Rec_Type_Ptr in a local vector inside the Ada function and then read/write record members? Does this approach has any fatalities?

推荐答案

在与Ada和C交互时，您应该真的阅读RM，附件 B.3 ，它表示：

When interfacing Ada and C, you should really read the RM, Annex B.3, which says:

任何类型的记录类型T的Ada参数，除了约定类型C_Pass_By_Copy的in参数外，作为at *参数传递给C函数，其中t是与Ada类型T相对应的C结构。。 p>

An Ada parameter of a record type T, of any mode, other than an in parameter of a type of convention C_Pass_By_Copy, is passed as a t* argument to a C function, where t is the C struct corresponding to the Ada type T.

因此，在您的过程中，只需执行以下操作即可：

So, in your procedure, just do:

procedure Process_Data (Edit_Result : in out Edit_Result_Rec_Type) is
begin
   Edit_Result.Status     := 1;
   Edit_Result.Error_Code := 0;
end Process_Data;

和

pragma Export(C, Process_Data);

（或使用方面，如果Ada 2012）

(or use the aspect, if Ada 2012)

话虽如此，您不应该在记录定义中使用Integer，Interfaces.C.int才是可行的方法：

That being said, you shouldn't use Integer in your record definition, Interfaces.C.int is the way to go:

type Edit_Result_Rec_Type is
   record
      Status     : Interfaces.C.int;
      Error_Code : Interfaces.C.int;
   end record;

将与您平台上的C int匹配（假设您的C编译器与Ada编译器兼容）

which will match the C int on your platform (assuming your C compiler is compatible with the Ada compiler)

关于您的问题：

1. 那可以，但是为什么要弄乱指针？

1. That would work, but why mess around with pointers?

不，那是行不通的，Ada中的访问类型（和访问值）不是地址。将 System.Address 转换为访问值需要 System.Address_To_Access_Conversions ，但是，为什么还要弄乱指针呢？ / p>

No, that wouldn't work, access types (and access values) in Ada are not addresses. Converting a System.Address to an access value requires System.Address_To_Access_Conversions, but again, why mess around with pointers?

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