DISPPARAMS

DISPPARAMS is a COM structure used by IDispatch::Invoke to supply arguments for a method call or property access on a dispatch interface. It is defined in OLE Automation and is used by automation clients and servers to marshal calls across process or apartment boundaries.

The structure consists of four fields. rgvarg is a pointer to an array of VARIANTARG structures that hold the arguments. The arguments are stored in reverse order: rgvarg[0] contains the last parameter, and rgvarg[cArgs-1] contains the first. rgdispidNamedArgs is a pointer to an array of DISPIDs that identify named arguments. cNamedArgs specifies how many named arguments are present, and there are cNamedArgs entries in rgdispidNamedArgs. cArgs is the total number of arguments, including named ones.

If there are no named arguments, cNamedArgs is zero and rgdispidNamedArgs is typically null. When named arguments are used, the values for the named arguments are located in rgvarg[cArgs - cNamedArgs] through rgvarg[cArgs - 1], corresponding to the DISPIDs in rgdispidNamedArgs[0] through rgdispidNamedArgs[cNamedArgs-1].

Common usage examples include property puts, where a named argument DISPID_PROPERTYPUT is used. For a property put with a single value argument, you would set cArgs = 1, cNamedArgs = 1, rgdispidNamedArgs[0] = DISPID_PROPERTYPUT, and rgvarg[0] holding the value to assign. Proper initialization and cleanup of VARIANTARG elements are required, including correct handling of BSTRs and interface pointers.