在Delphi中从C ++ DLL调用回调函数 [英] Calling a callback function in Delphi from a C++ DLL

问题描述

我有一个我写的C ++ DLL，它有一个单独的暴露的函数，它将一个函数指针（回调函数）作为参数。

  #define DllExport externC__declspec（dllexport）
 
 DllExport bool RegisterCallbackGetProperty（bool（* GetProperty）（UINT object_type，UINT object_instnace，UINT property_identifer，UINT device_identifier，float * value））{
 //执行某些操作。 
} 
  

我想能够从Delphi内调用这个暴露的C ++ DLL函数应用并注册将来使用的回调函数。但我不确定如何在Delphi中创建一个函数指针，该函数指针可以使用暴露的C ++ DLL函数。

我有 Delphi应用程序调用一个简单的暴露的c ++ DLL函数从我在这个问题的帮助。

我正在构建C ++ DLL，如果需要，我可以更改其参数。

我的问题是：

• 如何在Delphi中创建一个函数指针


• 如何从Delphi应用程序中正确调用暴露的C ++ DLL函数，以便C ++ DLL函数可以使用函数指针。

解决方案

通过声明函数类型在Delphi中声明一个函数指针。例如，您的回调的函数类型可以这样定义：

  type 
 TGetProperty = function（object_type，object_instnace，property_identifier，device_identifier：UInt; value：PSingle）：Boolean; CDECL; 
  

请注意，调用约定为 cdecl ，因为您的C ++代码指定没有调用约定，而cdecl是C ++编译器通常的默认调用约定。

然后可以使用该类型定义DLL函数：

  function RegisterCallbackGetProperty（GetProperty：TGetProperty）：Boolean; CDECL;外部'dllname'; 
  

将'dllname'替换为您的DLL。

要调用DLL函数，您应该首先具有与回调类型匹配的签名的Delphi函数。例如：

  function Callback（object_type，object_instnace，property_identifier，device_identifier：UInt; value：PSingle ）：Boolean cdecl; 
 begin 
结果：= False; 
结束
  

然后可以调用DLL函数并传递回调，就像其他变量一样： p>

  RegisterCallbackGetProperty（Callback）; 
  

I have a C++ DLL that I wrote that has a single exposed function, that takes a function pointer (callback function) as a parameter.

#define DllExport   extern "C" __declspec( dllexport )

DllExport bool RegisterCallbackGetProperty( bool (*GetProperty)( UINT object_type, UINT object_instnace, UINT property_identifer, UINT device_identifier, float * value ) ) {
    // Do something. 
}

I want to be able to call this exposed C++ DLL function from within a Delphi application and register the callback function to be used at a future date. But I am unsure of how to make a function pointer in Delphi that will work with the exposed C++ DLL function.

I have the Delphi application calling a simple exposed c++ DLL functions from the help I got in this question.

I am building the C++ DLL and I can change its parameters if needed.

My questions are:

• How to I create a function pointer in Delphi
• How to I correctly call the exposed C++ DLL function from within a Delphi application so that the C++ DLL function can use the function pointer.

解决方案

Declare a function pointer in Delphi by declaring a function type. For example, the function type for your callback could be defined like this:

type
  TGetProperty = function(object_type, object_instnace, property_identifier, device_identifier: UInt; value: PSingle): Boolean; cdecl;

Note the calling convention is cdecl because your C++ code specified no calling convention, and cdecl is the usual default calling convention for C++ compilers.

Then you can use that type to define the DLL function:

function RegisterCallbackGetProperty(GetProperty: TGetProperty): Boolean; cdecl; external 'dllname';

Replace 'dllname' with the name of your DLL.

To call the DLL function, you should first have a Delphi function with a signature that matches the callback type. For example:

function Callback(object_type, object_instnace, property_identifier, device_identifier: UInt; value: PSingle): Boolean cdecl;
begin
  Result := False;
end;

Then you can call the DLL function and pass the callback just as you would any other variable:

RegisterCallbackGetProperty(Callback);

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