Calling Visual C++ DLL's functions from Delphi code

Question

In a Delphi program I'm using a DLL to control an external executable. The DLL is written in Visual C++. In C++ the code to use DLL is:

// defining pointer's type to a function compatible with 'launcher' function:
typedef int (WINAPI* PFI_HD_ST_N)(HDC, LPCSTR, int);
…
…
HINSTANCE m_hiDLLCTRL;  // handle to DLL instance
PFI_HD_ST_N pfStart;    // pointer to function that starts external program

// initialization
m_hiDLLCTRL = NULL;
pfStart = NULL;

// links DLL dynamically
m_hiDLLCTRL = LoadLibrary(“ExtProgCTRL.dll”);

// if DLL has been loaded
If (m_hiDLLCTRL)
    // I get the address to funcion that launches ExtProg
    pfStart = ( PFI_HD_ST_N) GetProcAddress( m_hiDLLCTRL, “ExtProgStart” );
// launches external program
If ( pfStart )
    // hWnd is handle to window where I want do draw 
    pfStart -> ( GetDC ( hWnd ), “C:\\Programs\\ExtProg”, 1 );

I have an equivalent code in Delphi:

private
    DLLHandle: THandle;
    XInt: function: Integer: cdecl;

...
implementation
...
...
DLLHandle := LoadLibrary('ExtProgCTRL.dll');
if DLLHandle <> 0 then
begin
    @XInt := GetProcAddress(DLLHandle, ''ExtProgStart);
    if @XInt <> nil then
    begin
        MessageDlg('Function ExtProgStart loaded !', mtError, mbOKCancel, 0);
        ...
        ...
    end;
end;

It seems to work correctly, but I'm not able to find the Delphi code for the last instruction, to launch external program...

pfStart -> ( GetDC ( hWnd ), “C:\\Programs\\ExtProg”, 1 );

what in Delphi ?

I have changed:

private
    DLLHandle: THandle;
    XInt: function(DC: HDC; Text: PAnsiChar; SomeInt: Integer); Integer: cdecl;

...
implementation
...
retval: Integer;

DLLHandle := LoadLibrary('ExtProgCTRL.dll');
if DLLHandle <> 0 then
begin
    @XInt := GetProcAddress(DLLHandle, ''ExtProgStart);
    if @XInt <> nil then
    begin
        MessageDlg('Function ExtProgStart loaded !', mtError, mbOKCancel, 0);
       retval := XInt(GetDC(hWnd), 'C:\Programs\ExtProg', 1);
    end;
end;

but now I have on last instruction : retval := XInt... the following error: DCC Error : '(' expected but ')' found (parenthesis after hWnd)

It looks like you've retyped some of this rather than using copy/paste. pfStart -> ( GetDC ( hWnd ), “C:\\Programs\\ExtProg”, 1 ) is a syntax error I think and some of your quotes are messed up. I think I know what you mean, but using the clipboard helps us be sure we can see the exact same thing that you can see. — David Heffernan
– David Heffernan, Commented May 25, 2012 at 12:27

David Heffernan · Accepted Answer · 2012-05-25 12:42:01Z

3

You need to declare XInt like this:

XInt: function(DC: HDC; Text: PAnsiChar; SomeInt: Integer): Integer; stdcall;

You need to declare a parameter list that matches the definition in the C++ code.
I don't know meaningful names for the parameters but I'm sure you can supply them.
The C++ code specifies the WINAPI calling convention which matches stdcall in Delphi.

And then you can call it like this:

retval := XInt(GetDC(hWnd), 'C:\Programs\ExtProg', 1);

edited May 25, 2012 at 12:42

answered May 25, 2012 at 12:21

David Heffernan

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3 Comments

henry60 Over a year ago

I have changed as You suggested. Delphi gives an error on instruction retval := XInt... GetDC(hWnd) isn't recognized ...

David Heffernan Over a year ago

You didn't show all the code. So I can't see what you are looking at. What is not recognized?

David Heffernan Over a year ago

You need to get a window handle, hwnd, say. I can't work out where you'll get that from. I think I answered the question you asked.

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