Question

I am trying to create a DLL in C++ and export a function.

This is my C++ code:

#include <Windows.h>

void DLLMain(){

}

__declspec(dllexport) void xMain(){
MessageBox(NULL,L"Test",L"Test",NULL);
}

This is my delphi code:

program prjTestDllMain;

Uses
  Windows;

Var
  xMainPrc:procedure;stdcall;
  handle : THandle;
begin
    handle := LoadLibrary('xdll.dll');
    if handle <> 0 then
    begin
        MessageBox(0,'DLL Loaded', 0, 0);
        @xMainPrc := GetProcAddress(handle, 'xMain');
        if @xMainPrc <> nil then
            MessageBox(0,'Function Loaded', 0, 0)
        else
          MessageBox(0,'Function Not Loaded', 0, 0);
        MessageBox(0,'Process End', 0, 0);
        FreeLibrary(handle);
    end else
      MessageBox(0,'DLL Not Loaded', 0, 0);
end.

I get a messagebox for “DLL Loaded” just fine. But I get “Function Not Loaded” afterwards. What am I doing wrong here?

Answer 1

You can export it as a C function (__cdecl), so that it has a nice name on the exports table.

Name-decoration convention:
Underscore character (_) is prefixed to names, except when exporting __cdecl functions that use C linkage.

So basically, your function will have the name xMain in the exports table.

extern "C" __declspec(dllexport) void xMain()

And in the Delphi part, you just specify cdecl and call it normally:

var
  xMainPrc: procedure; cdecl;

For example:

if @xMainPrc <> nil then
begin
  MessageBox(0,'Function Loaded', 0, 0);
  xMainPrc;
end;