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POProblem getting correct parameters for C# P/Invoke call to C++ dll
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  1. POProblem getting correct parameters for C# P/Invoke call to C++ dll
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    copied!<p>Trying to Interop a functionality from the Outside In API from Oracle. Have the following function: </p> <pre><code>SCCERR EXOpenExport {VTHDOC hDoc, VTDWORD dwOutputId, VTDWORD dwSpecType, VTLPVOID pSpec, VTDWORD dwFlags, VTSYSPARAM dwReserved, VTLPVOID pCallbackFunc, VTSYSPARAM dwCallbackData, VTLPHEXPORT phExport); </code></pre> <p>From the header files I reduced the parameters to:<br> typedef VTSYSPARAM VTHDOC, VTLPHDOC *<br> typedef DWORD_PTR VTSYSPARAM<br> typedef unsigned long DWORD_PTR </p> <pre><code>typedef unsigned long VTDWORD typedef VTVOID* VTLPVOID #define VTVOID void typedef VTHDOC VTHEXPORT, *VTLPEXPORT These are for 32 bit windows </code></pre> <p>Going through the header files, the example programs, and the documentation I found:<br> 1. That pSpec could be a pointer to a buffer or NULL, so I set it to a IntPtr.Zero (documentation).<br> 2. That dwFlags and dwReserved according to the documentation "Must be set by the developer to 0".<br> 3. That pCallbackFunc can be set to NULL if I don't want to handle callbacks.<br> 4. That the last two are based on structs that I wrote C# wrappers for using the [StructLayout(LayoutKind.Sequential)]. Then instatiated an instance and generated the parameters by first creating a IntPtr with Marshal.AllocHGlobal(Marshal.SizeOf(instance)), then getting the address value which is passed as a uint for dwCallbackData and a IntPtr for phExport. </p> <p>The final parameter list is as follows: 1. phDoc as a IntPtr which was loaded with an address by the DAOpenDocument function called before.<br> 2. dwOutputId as uint set to 1535 which represents FI_JPEGFIF<br> 3. dwSpecType as int set to 2 which represents IOTYPE_ANSIPATH<br> 4. pSpec as an IntPtr.Zero where the output will be written<br> 5. dwFlags as uint set to 0 as directed<br> 6. dwReserved as uint set to 0 as directed<br> 7. pCallbackFunc as IntPtr set to NULL as I will handle results<br> 8. dwCallBackDate as uint the address of a buffer for a struct<br> 9. phExport as IntPtr to another struct buffer </p> <p>still get an undefined error from the API. Meaning that the call returns a 961 which is not defined in any of the header files. In the past I have gotten this when my choice of parameter types are incorrect.<br> I started out using Interop Assistant which was helpful in learning how many of the parameter types get translated. It is however limited by how well I am able to glean the correct native type from the header files. For example the hDoc parameter used in the preceding function was defined as a non-filesytem handle, so attempted to use Marshal to create a handle, then used an IntPtr, and finally it turned out to be an int (actually it was &amp;phDoc used here).<br> So is there a more scientific way of doing this, other than trial and error?<br> Jim</p>
 

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