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)

Answer 1

You need to declare XInt like this:

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

1. You need to declare a parameter list that matches the definition in the C++ code.
2. I don’t know meaningful names for the parameters but I’m sure you can supply them.
3. 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);