将Ada与C接口-从wchar\u t获取宽字符串*
我正在使用hidraw连接到一个USB设备（Debian Stretch上），我需要处理USB设备以将Ada与C接口-从wchar\u t获取宽字符串*,ada,gnat,Ada,Gnat,我正在使用hidraw连接到一个USB设备（Debian Stretch上），我需要处理USB设备以wchar\u t*的形式提供的一些信息，我需要将这些信息转换为（Ada）Wide\u String。这给我带来了一些麻烦，我没有看到一个干净的方法来使用Interfaces.C和Interfaces.C.Strings中的工具 所有文件都会向下编辑，而不会破坏其一致性。他们会建造，但如果没有，他们实际上不会运行 问题是，Linux设备驱动程序将诸如序列号和产品名称之类的设备信息显示为访问stdd
wchar\u t*Wide\u StringInterfaces.CInterfaces.C.Strings序列号产品名称访问stddef_h.wchar_t宽字符串函数值（项：在chars\u ptr中）返回字符串但我看不到宽字符串的等效项。所以我想我需要一个等价的值
函数来处理宽字符
下面的方法使用To_Ada
（来自Interfaces.C）返回给定wchar\u数组的宽字符串。当然，它失败了，因为访问wchar\u t
不能转换为wchar\u数组
-- helper function to deal with wchar_t * to wide_string
function Value (P : access stddef_h.wchar_t) return Wide_String is
temp : Wide_String(1 .. 256);
count : natural := 0;
-- ugliness to convert pointer types
type sd_wchar_ptr is access all stddef_h.wchar_t;
type wchar_array_ptr is access wchar_array;
Function To_Wchar_Array_Ptr is new Ada.Unchecked_Conversion(sd_wchar_ptr, wchar_array_ptr);
-- this does NOT create the required wchar_array pointer
WCP : wchar_array_ptr := To_Wchar_Array_Ptr(sd_wchar_ptr(P));
begin
Put_Line("Wide string");
To_Ada(WCP.all, temp, count);
Put_Line("Wide string length " & natural'image(count));
return temp(1..count);
end Value;
这是必然的结果
/测试\u hid
宽弦
由未处理的异常引发的存储错误终止执行：
堆栈溢出或错误的内存访问
类似的逐个字符的方法是可能的。。。如果（我真不敢相信我会这么说！）您可以增加访问类型
感觉界面缺少了一些东西。这里是C。。。我错过了什么？有没有办法绕过这个看似微不足道的绊脚石
编辑：我倾向于对Interfaces.C.Strings
源代码进行一些无耻的盗用，并进行了适当的修改，但我欢迎其他建议
下面的其余部分是到目前为止的完整故事（包括复制所需的所有代码）
步骤1：使用gcc自动生成低级Ada绑定
gcc-c-fdump ada spec slim/usr/include/hidapi/hidapi.h
生成低级别绑定包hidapi\u hidapi\u h
pragma Ada_2005;
pragma Style_Checks (Off);
with Interfaces.C; use Interfaces.C;
with Interfaces.C.Strings;
with stddef_h;
with System;
package hidapi_hidapi_h is
-- see source file /usr/include/hidapi/hidapi.h
type hid_device_info is record
path : Interfaces.C.Strings.chars_ptr; -- /usr/include/hidapi/hidapi.h:51
vendor_id : aliased unsigned_short; -- /usr/include/hidapi/hidapi.h:53
product_id : aliased unsigned_short; -- /usr/include/hidapi/hidapi.h:55
serial_number : access stddef_h.wchar_t; -- /usr/include/hidapi/hidapi.h:57
release_number : aliased unsigned_short; -- /usr/include/hidapi/hidapi.h:60
manufacturer_string : access stddef_h.wchar_t; -- /usr/include/hidapi/hidapi.h:62
product_string : access stddef_h.wchar_t; -- /usr/include/hidapi/hidapi.h:64
usage_page : aliased unsigned_short; -- /usr/include/hidapi/hidapi.h:67
usage : aliased unsigned_short; -- /usr/include/hidapi/hidapi.h:70
interface_number : aliased int; -- /usr/include/hidapi/hidapi.h:75
next : access hid_device_info; -- /usr/include/hidapi/hidapi.h:78
end record;
pragma Convention (C_Pass_By_Copy, hid_device_info); -- /usr/include/hidapi/hidapi.h:49
function hid_enumerate (arg1 : unsigned_short; arg2 : unsigned_short) return access hid_device_info; -- /usr/include/hidapi/hidapi.h:132
pragma Import (C, hid_enumerate, "hid_enumerate");
end hidapi_hidapi_h;
这是一个低级绑定，公开C类型（绑定生成器已决定接口中的wchar\u t
。C
不够好，它还需要stddef.h
中的一个，因此
pragma Ada_2005;
pragma Style_Checks (Off);
with Interfaces.C; use Interfaces.C;
package stddef_h is
-- unsupported macro: NULL ((void *)0)
subtype size_t is unsigned_long; -- /usr/lib/gcc/x86_64-linux-gnu/6/include/stddef.h:216
subtype wchar_t is int; -- /usr/lib/gcc/x86_64-linux-gnu/6/include/stddef.h:328
end stddef_h;
因为它是一个低级绑定；我们希望将它隐藏（并实现RAII等）在一个更简单、更可用的高级绑定后面，所以…（下面）
及其实现，包含返回宽字符串的问题函数value
with hidapi_hidapi_h;
with Interfaces.C; use Interfaces.C;
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Unchecked_Conversion;
with stddef_h;
package body hidapi is
function enumerate (vendor_id, product_id : id) return hid_device is
use hidapi_hidapi_h;
first : access hid_device_info;
begin
first := hid_enumerate(unsigned_short(vendor_id), unsigned_short(product_id));
if first /= null then
return H : hid_device do
H.member := first;
H.addr := System.Null_Address;
end return;
else raise Program_Error;
end if;
end enumerate;
-- helper function to deal with wchar_t * to wide_string
function Value (P : access stddef_h.wchar_t) return Wide_String is
temp : Wide_String(1 .. 256);
count : natural := 0;
type sd_wchar_ptr is access all stddef_h.wchar_t;
type wchar_array_ptr is access wchar_array;
Function To_Wchar_Array_Ptr is new Ada.Unchecked_Conversion(sd_wchar_ptr, wchar_array_ptr);
WCP : wchar_array_ptr := To_Wchar_Array_Ptr(sd_wchar_ptr(P));
begin
Put_Line("Wide string");
To_Ada(WCP.all, temp, count);
Put_Line("Wide string length " & natural'image(count));
return temp(1..count);
end Value;
function Serial_No (D : hid_device) return Wide_String is
use hidapi_hidapi_h;
begin
return Value(D.member.serial_number);
end Serial_No;
function Product_String (D : hid_device) return Wide_String is
use hidapi_hidapi_h;
begin
return Value(D.member.product_string);
end Product_String;
end hidapi;
当然还有一个测试用例来练习它
with Hidapi;
with Ada.Wide_Text_IO;
procedure Test_Hid is
usbrelay_vendor_id : constant Hidapi.id := 16#16c0#;
usbrelay_product_id : constant Hidapi.id := 16#05df#;
Device : Hidapi.hid_device := Hidapi.Enumerate(usbrelay_vendor_id, usbrelay_product_id);
begin
Ada.Wide_Text_IO.Put_Line("Serial : " & Device.Serial_No);
Ada.Wide_Text_IO.Put_Line("Product : " & Device.Product_String);
end Test_Hid;
一个答案是，在对Tnterfaces.C.Strings
进行必要更改的情况下，盲目地复制包体中的方法
顽皮的东西在函数“+”
和Peek
中，它们在指针上使用未经检查的转换
- 允许地址运算。不是指针增量，而是指针+偏移量。一个变化是偏移量必须缩放为4字节字符。我没有以可移植的方式设置这种缩放，但请注意，
“+”
将为每个不同的返回类型重载，以便为不同的命名访问类型适当缩放偏移量
- 在没有任何类型转换函数的情况下，允许将
stddef_h.wchar_t
视为Wide_Wide_字符
。表示是否正确是另一回事（这里是）但是这种技术也可以用来伪造接口中合适的转换函数的输入类型，如到_Ada
剩下的是简单的逐字符处理。另一个变化（到目前为止）是返回Wide\u Wide\u character
，而不是Wide\u character
（因为正如上面的stddef_h
包所示，存储的字符是32位的，与Interfaces.C.int
大小相同。我很乐意更改我的接口，但是宽字符串可以由Ada.Strings
包轻松处理
type sd_wchar_ptr is access all stddef_h.wchar_t;
type w_w_char_ptr is access all char32_t;
-- Two Unchecked_Conversions to allow pointer arithmetic
-- And a third to allow the resulting storage to be interpreted as Wide_Wide_Char
function To_Sd_wchar_ptr is new Ada.Unchecked_Conversion (System.Address, sd_wchar_ptr);
function To_Address is new Ada.Unchecked_Conversion (sd_wchar_ptr, System.Address);
function To_Wchar_Ptr is new Ada.Unchecked_Conversion (sd_wchar_ptr, w_w_char_ptr);
-- pointer + offset arithmetic, with offset scaled for size of stddef_h.wchar_t;
-- TODO: attempted better way of computing word size ran into type errors
function "+" (Left : sd_wchar_ptr; Right : size_t) return sd_wchar_ptr is
begin
return To_Sd_wchar_ptr (To_Address (Left) + Storage_Offset (Right) * 4);
end "+";
function Peek (From : sd_wchar_ptr) return char32_t is
begin
return To_Wchar_Ptr(From).all;
end Peek;
function Strlen (Item : sd_wchar_ptr) return size_t is
Item_Index : size_t := 0;
begin
if Item = Null then
raise Program_Error;
end if;
loop
if Peek (Item + Item_Index) = char32_nul then
return Item_Index;
end if;
Item_Index := Item_Index + 1;
end loop;
end Strlen;
function Value (Item : sd_wchar_ptr) return char32_array is
Result : char32_array (0 .. Strlen (Item));
begin
if Item = Null then
raise Program_Error;
end if;
Put_Line("String length " & size_t'image(Strlen(Item)));
-- Note that the following loop will also copy the terminating Nul
for J in Result'Range loop
Result (J) := Peek (Item + J);
end loop;
return Result;
end Value;
-- helper function to deal with wchar_t * to wide_wide_string
function Value (Item : access stddef_h.wchar_t) return Wide_Wide_String is
begin
return To_Ada (Value (sd_wchar_ptr(Item)));
end Value;
type sd_wchar_ptr is access all stddef_h.wchar_t;
type w_w_char_ptr is access all char32_t;
-- Two Unchecked_Conversions to allow pointer arithmetic
-- And a third to allow the resulting storage to be interpreted as Wide_Wide_Char
function To_Sd_wchar_ptr is new Ada.Unchecked_Conversion (System.Address, sd_wchar_ptr);
function To_Address is new Ada.Unchecked_Conversion (sd_wchar_ptr, System.Address);
function To_Wchar_Ptr is new Ada.Unchecked_Conversion (sd_wchar_ptr, w_w_char_ptr);
-- pointer + offset arithmetic, with offset scaled for size of stddef_h.wchar_t;
-- TODO: attempted better way of computing word size ran into type errors
function "+" (Left : sd_wchar_ptr; Right : size_t) return sd_wchar_ptr is
begin
return To_Sd_wchar_ptr (To_Address (Left) + Storage_Offset (Right) * 4);
end "+";
function Peek (From : sd_wchar_ptr) return char32_t is
begin
return To_Wchar_Ptr(From).all;
end Peek;
function Strlen (Item : sd_wchar_ptr) return size_t is
Item_Index : size_t := 0;
begin
if Item = Null then
raise Program_Error;
end if;
loop
if Peek (Item + Item_Index) = char32_nul then
return Item_Index;
end if;
Item_Index := Item_Index + 1;
end loop;
end Strlen;
function Value (Item : sd_wchar_ptr) return char32_array is
Result : char32_array (0 .. Strlen (Item));
begin
if Item = Null then
raise Program_Error;
end if;
Put_Line("String length " & size_t'image(Strlen(Item)));
-- Note that the following loop will also copy the terminating Nul
for J in Result'Range loop
Result (J) := Peek (Item + J);
end loop;
return Result;
end Value;
-- helper function to deal with wchar_t * to wide_wide_string
function Value (Item : access stddef_h.wchar_t) return Wide_Wide_String is
begin
return To_Ada (Value (sd_wchar_ptr(Item)));
end Value;