Calling PB/DLL from C

[Gregery D Engle]

I'm having some problems with the prototype in C

This is what I have so far:

typedef int __stdcall yoga( char &strMessage, 
                            char strAddressOut, 
                            char strAddress2Out, 
                            char strSubject );

and this is what I get during build:

d:\packet\wpdpack\examples\testapp\pbdll.h(1) : error C2143: syntax error : missing ')' before '&'
d:\packet\wpdpack\examples\testapp\pbdll.h(1) : error C2143: syntax error : missing '{' before '&'
d:\packet\wpdpack\examples\testapp\pbdll.h(1) : error C2059: syntax error : '&'
d:\packet\wpdpack\examples\testapp\pbdll.h(1) : error C2059: syntax error : ')'

------------------
-Greg

[Tom Hanlin]

A typedef of that nature would be for calling a function loaded using
LoadLibrary... is that what you have in mind? I'm pretty rusty at C
calls designed in that fashion, so I'm unlikely to get this quite right,
but perhaps I can help a bit.

In C, a "char" is a signed byte type. An ampersand ("&") works much
like the PowerBASIC function VARPTR, although the ampersand evaluates
like a pseudo-op rather than a function. It seems probable that there
are serious things wrong with your C declaration, although it's not
fully clear what you intend without seeing the PB function header.
If you intend a C string, you need to declare a char pointer, or "char *"
in C, and use an ASCIIZ string in PowerBASIC.

Assuming that your PowerBASIC function looks something like this:

FUNCTION yoga ALIAS "yoga" (strMessage AS ASCIIZ, strAddressOut AS ASCIIZ, _
    strAddress2Out AS ASCIIZ, strSubject AS ASCIIZ) EXPORT AS LONG

Your C declaration should look more like this:

typedef int __stdcall yoga (char * strMessage, char * strAddressOut, \
    char * strAddress2Out, char * strSubject);

Seems to me that you need a few extra parentheses in the C code and,
perhaps, a little bit of redesign for the typedef. I'll see if I can dig
up the particulars tomorrow, if no one else has been able to clarify all
this by then.

------------------
Tom Hanlin
PowerBASIC Staff

[Peter P Stephensen]

This should do it:

#include <windows.h>
 
typedef int (_stdcall *LPYOGA)(char *,char *,char *,char *); 
 
int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
	HINSTANCE hDll;
	LPYOGA Yoga;
 
	if((hDll = LoadLibrary("YourDll.dll")) == NULL) 
	{
		MessageBox(0, "Could not load YourDll.dll","Test", MB_OK);
		return 0;
	}
 
	if((Yoga = (LPYOGA)GetProcAddress(hDll, "Yoga")) == NULL)
	{	
		FreeLibrary(hDll);
		MessageBox(0, "Could not load function Yoga","Test", MB_OK);
		return 0;	
	}
 
	//Use function
	int i = Yoga("This", "Is", "a", "test");
 	
	FreeLibrary(hDll);
	return 0;
}

Regards
Peter

------------------

[Gregery D Engle]

I'm writing a packet sniffer and it seems that all examples are
in C so, I'm modifying the examples to perform what I want, (already
done) and then I'm simply going to call a PB/DLL for every packet
that is received. I think it will be much easier.

In that case don't I want BYREF instead of BYVAL?

Actually I think the function will be more like this:

function PacketSniff(byref hexdata as dword) as long

But I think I can modify the C typedef you provided me.

Thanks

------------------
-Greg

[This message has been edited by Gregery D Engle (edited January 16, 2001).]