DispInvoke function (oleauto.h)

Article
04/02/2021

Automatically calls member functions on an interface, given the type information for the interface. You can describe an interface with type information and implement Invoke for the interface using this single call.

Syntax

HRESULT DispInvoke(
  void       *_this,
  ITypeInfo  *ptinfo,
  DISPID     dispidMember,
  WORD       wFlags,
  DISPPARAMS *pparams,
  VARIANT    *pvarResult,
  EXCEPINFO  *pexcepinfo,
  UINT       *puArgErr
);

Parameters

_this

An implementation of the IDispatch interface described by ptinfo.

ptinfo

The type information that describes the interface.

dispidMember

The member to be invoked. Use GetIDsOfNames or the object's documentation to obtain the DISPID.

wFlags

Flags describing the context of the Invoke call.

Value	Meaning
DISPATCH_METHOD	The member is invoked as a method. If a property has the same name, both this and the DISPATCH_PROPERTYGET flag can be set.
DISPATCH_PROPERTYGET	The member is retrieved as a property or data member.
DISPATCH_PROPERTYPUT	The member is changed as a property or data member.
DISPATCH_PROPERTYPUTREF	The member is changed by a reference assignment, rather than a value assignment. This flag is valid only when the property accepts a reference to an object.

pparams

Pointer to a structure containing an array of arguments, an array of argument DISPIDs for named arguments, and counts for number of elements in the arrays.

pvarResult

Pointer to where the result is to be stored, or Null if the caller expects no result. This argument is ignored if DISPATCH_PROPERTYPUT or DISPATCH_PROPERTYPUTREF is specified.

pexcepinfo

Pointer to a structure containing exception information. This structure should be filled in if DISP_E_EXCEPTION is returned.

puArgErr

The index within rgvarg of the first argument that has an error. Arguments are stored in pdispparams->rgvarg in reverse order, so the first argument is the one with the highest index in the array. This parameter is returned only when the resulting return value is DISP_E_TYPEMISMATCH or DISP_E_PARAMNOTFOUND.

Return value

Return code	Description
S_OK	Success.
DISP_E_BADPARAMCOUNT	The number of elements provided to DISPPARAMS is different from the number of arguments accepted by the method or property.
DISP_E_BADVARTYPE	One of the arguments in DISPPARAMS is not a valid variant type.
DISP_E_EXCEPTION	The application needs to raise an exception. In this case, the structure passed in pexcepinfo should be filled in.
DISP_E_MEMBERNOTFOUND	The requested member does not exist.
DISP_E_NONAMEDARGS	This implementation of IDispatch does not support named arguments.
DISP_E_OVERFLOW	One of the arguments in DISPPARAMS could not be coerced to the specified type.
DISP_E_PARAMNOTFOUND	One of the parameter IDs does not correspond to a parameter on the method. In this case, puArgErr is set to the first argument that contains the error.
DISP_E_PARAMNOTOPTIONAL	A required parameter was omitted.
DISP_E_TYPEMISMATCH	One or more of the arguments could not be coerced. The index of the first parameter with the incorrect type within rgvarg is returned in puArgErr.
E_INVALIDARG	One of the parameters is not valid.
E_OUTOFMEMORY	Insufficient memory to complete the operation.

Any of the ITypeInfo::Invoke errors can also be returned.

Remarks

The parameter _this is a pointer to an implementation of the interface that is being deferred to. DispInvoke builds a stack frame, coerces parameters using standard coercion rules, pushes them on the stack, and then calls the correct member function in the VTBL.

Examples

The following code from the Lines sample file Lines.cpp implements Invoke using DispInvoke. This implementation relies on DispInvoke to validate input arguments. To help minimize security risks, include code that performs more robust validation of the input arguments.

STDMETHODIMP
CLines::Invoke(
   DISPID dispidMember,
   REFIID riid,
   LCID lcid,
   WORD wFlags,
   DISPPARAMS * pdispparams,
   VARIANT * pvarResult,
   EXCEPINFO* pexcepinfo,
   UINT * puArgErr)
{
   return DispInvoke(
   this, m_ptinfo,
   dispidMember, wFlags, pdispparams,
   pvarResult, pexcepinfo, puArgErr); 
}

Requirements

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

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