DispGetParam

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

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

Parameters

pdispparams: Pointer to the parameters passed to IDispatch::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.
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 Value

The return value obtained from the HRESULT is one of the following:

Return value	Meaning
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 arguments was invalid.
E_OUTOFMEMORY	Insufficient memory to complete operation.

Comments

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)

Named parameters cannot be accessed positionally, and vice versa.

Example

The following 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;
}

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