Need Help with COM object HEC-RAS

[FariborzNouri]

Need help with HEC-RAS
Hello
I am trying to run a COM application known as HEC-RAS from an unmanaged C++ program in Visual Studio. Classes have been added to the project by adding new MFC classes from a TypeLib. CoInitialize() has been called and interface has been created successfully. One particular method in one of the classes CHECRASControll er has the following signature in C++.

BOOL Compute_CurrentPlan(long * nmsg, SAFEARRAY * * msg); 
Using Object Browser this function is 
Function Compute_CurrentPlan(nmsg As Long, msg() As String) As Boolean.

In another project we used a mixture of VB and C++ and successfully called the above function, I found that the return parameter msg() is an array of 3 strings.

In C++ I wrote

   long pl;
   
   SAFEARRAYBOUND rgsabound[1];
   rgsabound[0].lLbound = 1;     // lower bound for indexing, in VB it would have been 1
   rgsabound[0].cElements = 3;   // from vb runs i found that 3 strings will be returned
   //SAFEARRAY *psa = SafeArrayCreate(VT_VARIANT, 1, rgsabound);
   SAFEARRAY *psa = SafeArrayCreate(VT_BSTR, 1, rgsabound);
   psa->fFeatures = FADF_BSTR | FADF_AUTO; //  | FADF_FIXEDSIZE;

I called the function as
hec.Compute_Cur rentPlan(&pl, &psa);

This causes an internal error, I also tried creating the SAFEARRAY with VT_NULL or VT_EMPTY as the element types by

   /* trying to see whether I can create it as VT_EMPTY or VT_NULL 
   SAFEARRAYBOUND rgsabound[1];
   rgsabound[0].lLbound = 1;     // lower bound for indexing, in VB it would have been 1
   rgsabound[0].cElements = 1;   // from vb runs i found that 3 strings will be returned
   SAFEARRAY *psa;
   psa = SafeArrayCreateEx(VT_EMPTY, 1, rgsabound, NULL);  //  VT_NULL
   */

Again no success. I will appreciate any help as I don’t have experience with COM objects.
Thanks in advance

[weaknessforcats]

It's been long time since I looked at COM but you might try:

rgsabound[0].lLbound = 0;    
rgsabound[0].cElements = 3;

I believe that is for a SAFEARRAY of 3 elements with a starting index of 0. Arrays in C/C++ start indexing at 0.

Let me know what happens.

[FariborzNouri]

Unfortunately that didn't work either. The source code of the function in the header file was

   BOOL Compute_CurrentPlan(long * nmsg, SAFEARRAY **msg)
   {
      BOOL result;
      static BYTE parms[] = VTS_PI4 VTS_UNKNOWN ;
      InvokeHelper(0x6003000b, DISPATCH_METHOD, VT_BOOL, (void*)&result, parms, nmsg, msg);
      return result;
   }

I noticed that parms[] has VTS_UNKNOWN so I went back and changed the safe array creation to

   SAFEARRAYBOUND rgsabound[1];
   rgsabound[0].lLbound = 0;     // lower bound for indexing, in VB it would have been 1
   rgsabound[0].cElements =3;   // from vb runs i found that 3 strings will be returned
   SAFEARRAY *psa = SafeArrayCreate(VT_UNKNOWN, 1, rgsabound);

That didn't work either. I am completely out of ideas now !!!

[weaknessforcats]

Did you actually put elements in your SAFEARRAY?

I took your code and created a SAFEARRAY of BSTR and then created three BSTR and then put those BSTRs in the SAFEARRAY.

I can see them in the SAFEARRAY using my debugger.

SAFEARRAYBOUND rgsabound[1]; 
   rgsabound[0].lLbound = 1;     // lower bound for indexing, in VB it would have been 1 
   rgsabound[0].cElements = 3;   // from vb runs i found that 3 strings will be returned 
   //SAFEARRAY *psa = SafeArrayCreate(VT_VARIANT, 1, rgsabound); 
   SAFEARRAY *psa = SafeArrayCreate(VT_BSTR, 1, rgsabound); 
   psa->fFeatures = FADF_BSTR | FADF_AUTO; //  | FADF_FIXEDSIZE;  

   BSTR x = SysAllocString(L"Hello");
   BSTR y = SysAllocString(L"this is a ");
   BSTR z = SysAllocString(L"COM test");

   //goes to ILbound =1, c.Elements = 1;
   rgsabound[0].cElements = 1; 
   HRESULT hr =  SafeArrayPutElement(psa, (long*)rgsabound, x);
   //goes to ILbound =1, c.Elements = 2;
    rgsabound[0].cElements = 2; 
   hr = SafeArrayPutElement(psa, (long*)rgsabound, y);
    //goes to ILbound =1, c.Elements = 3;
    rgsabound[0].cElements = 3; 
   hr = SafeArrayPutElement(psa, (long*)rgsabound, z);

I do not show the SysFreeString calls.