Calling a callback function in Delphi from a C++ DLL
c++, delphi, delphi-7, dll
Solution
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);
Problem
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.