DispGetParam function (oleauto.h)

Article
02/22/2024

Retrieves a parameter from the DISPPARAMS structure, checking both named parameters and positional parameters, and coerces the parameter to the specified type.

Syntax

HRESULT DispGetParam(
  [in]            DISPPARAMS *pdispparams,
                  UINT       position,
                  VARTYPE    vtTarg,
  [out]           VARIANT    *pvarResult,
  [out, optional] UINT       *puArgErr
);

Parameters

[in] pdispparams

The parameters passed to Invoke.

position

The 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

The type the argument should be coerced to.

[out] pvarResult

the variant to pass the parameter into.

[out, optional] puArgErr

On return, 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 value

This function can return one of these values.

Return code	Description
S_OK	Success.
DISP_E_BADVARTYPE	The variant type vtTarg is not supported.
DISP_E_OVERFLOW	The retrieved parameter could not be coerced to the specified type.
DISP_E_PARAMNOTFOUND	The parameter indicated by position could not be found.
DISP_E_TYPEMISMATCH	The argument could not be coerced to the specified type.
E_INVALIDARG	One of the parameters is not valid.
E_OUTOFMEMORY	Insufficient memory to complete the operation.

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.

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, &uiArg)

Named parameters cannot be accessed positionally, and vice versa.

Examples

The following example uses DispGetParam to set X and Y properties.

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

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

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

Requirements

Requirement	Value
Target Platform	Windows
Header	oleauto.h
Library	OleAut32.lib
DLL	OleAut32.dll