Hello,

OK, this is a first for me… I need some help with OI.

I am trying to make function calls to a VC++ DLL that I wrote a year ago (DirectPrint.DLL), and it works perfect with OI 4.x.

Here is the VC++ declaration:

#define DIRECTPRINT_API __declspec(dllexport)

DIRECTPRINT_API int DirectStart(LPSTR lpPrinterName, LPSTR lpTitle);

And here is the OI declaration:

INT STDCALL DirectStart(LPCHAR,LPCHAR)

And here is the line of code that fails in Basic+:

retval=DirectStart("","Test report")

When I call the DirectStart() function from Basic+, it works OK. But when I was debugging the VC++ DLL I discovered that string parameters (LPSTR) contained invalid data from OI. I though I might need to do a LockVariable and GetPointer, but that also failed to pass the string data from OI to my DLL correctly. I tried changing the calling convention in my VC++ DLL to C and Standard, and I tried other string data types (char *, LPCSTR, LPWSTR), but it did not help.

After closer examination of the data pointed to by the LPSTR, I discovered the problem – The strings were not NULL terminated. So I changed my Basic+ code to:

retval=DirectStart("":Char(0),"Test report":Char(0))

and everything started to work perfectly again!

So here is my question:

Does anyone know if the DLL calling wrapper in OI changed in version 7.0? Because it appears that previous versions automatically appended the NULL to LPCHAR parameters. I understand that it is a good idea to always terminate strings when calling DLLs, but it was not required in previous versions. It seems a bit painful to make us put the NULL on each string parameter.

Sincerely,

Tony Splaver

Splaver Software

Tony

Earlier OIs GPFed if the null wasn't there so I guess we just got into the habit of including it. Prototyping has been extended - check out SRPCS's White Paper on the subject at http://www.srpcs.com/resources/articles/DLL_Parameter_Types_in_OpenInsight.pdf.

The Sprezzatura Group

World Leaders in all things RevSoft

OI 4.x did not have any problems with non-NULL terminated strings (I think you are referring to OI16). I think it is a bit painful to require the NULL character on each string variable… for example, in VB you do not need to add the NULL character, because VB knows to always put it on for you when you declare a variable as String.

So I am wondering if OI 4.x had a "bug" that allowed you to not use the NULL, and they fixed it in 7.0.

You now have LPCHAR and LPSTR.

This is what Pat said:

"Only the return value of LPCHAR has to change if it really is a null-terminated string you want returned. The LPCHAR parameter works pretty much like it always has, although if you want the engine to automatically null-terminate the string for you, then you might want to use LPSTR."

Tony,

Read the white paper Sprezz linked to.

Pat

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