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Date Posted: 18:33:39 05/01/03 Thu
Author: Michel
Subject: Re: Testing Envision Image Library C Builder
In reply to: Don 's message, "Testing Envision Image Library C Builder" on 16:10:49 05/01/03 Thu


Hi Don,

I do not have a CBuilder demo complete like the example program. Usually the port from C++ to Object Pascal is quite straight forward, replacing TObject.Create with new TObject() from Free with Delete. Remember all VCL objects must be created explicitely in CBuiler.

I think the problem you are having is that your type TpScanInfo is not pointer type, but an "alias" for the structure. The convention I use is that a structure type has the format TStructure, and the typedef for a pointer to the structure is TpStructure. I know there are various ways to identify the name of a struct in C (whether you use straight C or C++ extensions), but I don't recall the exact differences.

The cast you have is trying to cast from an integer (CallBackData) to a user defined structure, to the compiler complains. This will probably work,

pScanInfo = TpScanInfo*(CallBackData);

The idea is that a pointer is 4 bytes just like an integer.

Note that a proper value (ie, the address of a TScanInfo structure) must be passed to TScanner->Acquire(), to use this call back data mechanism.

You can avoid the call back data mechanism, by simply holding the information globally on the form.

Best regards,

Michel
>I am testing your Library with C++ Builder 5 Pro. I am
>trying to create a C++ Builder App to test with based
>on your Delphi/Pas Demo. Do you have the same code in
>C++?
>Here is a sample of my code and the current error I am
>getting.
>
>In Header file:
>
>private: // User declarations
> void __fastcall OnAcquire( const THandle
>DibHandle, const unsigned short XDpi,
> const unsigned
>short YDpi, const int CallBackData);
> typedef struct TpScanInfo
> {
> bool MultiPage;
> const TTiffGraphic* Graphic;
> TFileStream *ScanStream;
> long int ImageCount;
> } TScanInfo;
>
>In CPP Unit:
>
>void __fastcall TForm1::OnAcquire( const THandle
>DibHandle, const unsigned short XDpi,
> const unsigned short YDpi,
>const int CallBackData)
>{
>
>TScanInfo *pScanInfo = new TScanInfo;
>pScanInfo = TpScanInfo(CallBackData);
>
>Here is where the error is generated:
>
>[C++ Error] MainUnit.cpp(77): E2031 Cannot cast from
>'const int' to 'TForm1::TpScanInfo'
>
>Thanks,
>
>Don

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