C++ struct to Delphi Record dll call

Question

I am trying to convert c++ struct to delphi Record for dll call

// c++ struct

typedef struct dll_info_t
{
   char version[32];
   char r_type[128];
   char b_date[32];
   char c_list[32];
   char build[32];
}dll_info_t;

LIBEX_EXPORT int LIB_API Dll_get_lib_info(dll_info_t* info);

// Delphi Converted

dll_info_t = record
 version:AnsiChar;
 r_type:AnsiChar;
 b_date:AnsiChar;
 c_list:AnsiChar;
 build:AnsiChar;
end;
        
Dll_get_lib_info: Function (info : dll_info_t) : Integer; stdcall;

var
  hHandle:THandle;
begin
  hHandle := LoadLibrary(Dl_path);
    @Dll_get_lib_info:=GetProcAddress(hHandle, PChar('Dll_get_lib_info'));

    if Assigned(Dll_get_lib_info) then begin
     Dll_get_lib_info(info);
     ShowMessage(info.version); // <- I Get Empty Output
     ShowMessage(info.release_type); // <- I Get Empty Output
     ShowMessage(info.build_date); // <- I Get Empty Output
     ShowMessage(info.change_list); // <- I Get Empty Output
    end;

end;

I get empty output

I am not sure if converted record is correct ?

I have checked online char in delphi is Ansichar ?

David Heffernan · Accepted Answer · 2020-06-20 13:09:58Z

2

char version[32] is not the same as AnsiChar, because that AnsiChar is a single character. You need an array of AnsiChar, (version: array [0..31] of AnsiChar) just like what is used in the C code. You'll need the proper declaration for all of the members of the record.

type
  dll_info_t = record
    version: array [0..31] of AnsiChar;
    r_type: array [0..127] of AnsiChar;
    b_date: array [0..31] of AnsiChar;
    c_list: array [0..31] of AnsiChar;
    build: array [0..31] of AnsiChar;
  end;

var 
  Dll_get_lib_info: Function(out info: dll_info_t): Integer; stdcall;
  hMod: HMODULE;
  info: dll_info_t;
begin
  hMod := LoadLibrary(Dl_path);
  @Dll_get_lib_info := GetProcAddress(hMod, 'Dll_get_lib_info');

  if Assigned(Dll_get_lib_info) then begin
    Dll_get_lib_info(info);
    ShowMessage(info.version);
    ShowMessage(info.release_type);
    ShowMessage(info.build_date);
    ShowMessage(info.change_list);
  end;
end;

Whether or not stdcall is correct depends on the definition of the LIB_API macro.

edited Jun 20, 2020 at 13:09

David Heffernan

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answered Jun 20, 2020 at 12:44

Ken White

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1 Comment

David Heffernan Over a year ago

@Maaz Note that you should add error checking on your Windows API calls, and possibly a call to FreeLibrary

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