DispGetParam

This function retrieves a parameter from the DISPPARAMS structure, checks both named parameters and positional parameters, and coerces the parameter to the specified type.

At a Glance

Syntax

HRESULT DispGetParam(DISPPARAMS FAR* pdispparams, unsigned int position, VARTYPE vtTarg, VARIANT FAR* pvarResult, unsigned int FAR* puArgErr);

Parameters

pdispparams

Pointer to the parameters passed to IDispatch::Invoke.

position

Position of the parameter in the parameter list. DispGetParam starts at the end of the array, so if position is 0, the last parameter in the array is returned.

vtTarg

Type the argument should be coerced to.

pvarResult

Pointer to the variant to pass the parameter into.

puArgErr

On return, pointer to the index of the argument that caused a DISP_E_TYPEMISMATCH error. This pointer is returned to Invoke to indicate the position of the argument in DISPPARAMS that caused the error.

Return Values

One of the values obtained from the returned HRESULT and described in the following table is returned.

Remarks

The output parameter pvarResult must be a valid variant. Any existing contents are released in the standard way. The contents of the variant are freed with VariantFree.

Passing into this function any invalid and, under some circumstances, NULL pointers will result in unexpected termination of the application.

If you have used DispGetParam to get the right side of a property put operation, the second parameter should be DISPID_PROPERTYPUT. For example:

DispGetParam(&dispparams, DISPID_PROPERTYPUT, VT_BOOL, &varResult)

Named parameters cannot be accessed positionally, and vice versa.

Example

The following code example uses DispGetParam to set X and Y properties:

STDMETHODIMP
CPoint::Invoke(
   DISPID dispidMember,
   REFIID riid,
   LCID lcid,
   unsigned short wFlags,
   DISPPARAMS FAR* pdispparams,
   VARIANT FAR* pvarResult,
   EXCEPINFO FAR* pExcepInfo,
   unsigned int FAR* puArgErr)
{
   unsigned int uArgErr;
   HRESULT hresult;
   VARIANTARG varg0;
   VARIANT varResultDummy;

   UNUSED(lcid);
   UNUSED(pExcepInfo);

   // Make sure the wFlags are valid.
   if(wFlags & ~(DISPATCH_METHOD | DISPATCH_PROPERTYGET |
      DISPATCH_PROPERTYPUT | DISPATCH_PROPERTYPUTREF))
      return ResultFromScode(E_INVALIDARG);

   // This object only exposes a "default" interface.
   if(!IsEqualIID(riid, IID_NULL))
      return ResultFromScode(DISP_E_UNKNOWNINTERFACE);

   // It simplifies the following code if the caller
   // ignores the return value.
   if(puArgErr == NULL)
      puArgErr = &uArgErr;
   if(pvarResult == NULL)
      pvarResult = &varResultDummy;

   VariantInit(&varg0);

   // Assume the return type is void, unless otherwise is found.
   VariantInit(pvarResult);

   switch(dispidMember){
   case IDMEMBER_CPOINT_GETX:
      V_VT(pvarResult) = VT_I2;
      V_I2(pvarResult) = GetX();
      break;

   case IDMEMBER_CPOINT_SETX:
      HRESULT = DispGetParam(pdispparams, 0, VT_I2, &varg0, puArgErr);
      if(HRESULT != NOERROR)
         return hresult;
      SetX(V_I2(&varg0));
      break;

   case IDMEMBER_CPOINT_GETY:
      V_VT(pvarResult) = VT_I2;
      V_I2(pvarResult) = GetY();
      break;

   case IDMEMBER_CPOINT_SETY:
      HRESULT = DispGetParam(pdispparams, 0, VT_I2, &varg0, puArgErr);
      if(HRESULT != NOERROR)
         return hresult;
      SetY(V_I2(&varg0));
      break;

   default:
      return ResultFromScode(DISP_E_MEMBERNOTFOUND);
   }
   return NOERROR;
}