pDispParams

pDispParams is a pointer to a DISPPARAMS structure used by the IDispatch::Invoke method in COM automation. It carries the actual arguments for a late-bound call, including both positional and named parameters, as provided by the caller.

The DISPPARAMS structure contains four fields: rgvarg, rgdispidNamedArgs, cArgs, and cNamedArgs. rgvarg is a pointer to an array of VARIANTARG values that represent the argument values. cArgs is the total number of arguments in this array. If named arguments are used, rgdispidNamedArgs points to an array of DISPIDs that identify those named arguments, and cNamedArgs specifies how many of the arguments are named. The layout and interpretation of these fields are defined by the COM automation conventions.

Arguments are stored in rgvarg in reverse order. The first element in rgvarg holds the last argument passed to the method, and the last element holds the first. When invoking a method with named arguments, the corresponding DISPIDs in rgdispidNamedArgs indicate which elements of rgvarg correspond to the named parameters, and cNamedArgs provides the count of such named arguments. This means parameter access by the callee follows a predictable mapping from the DISPID lists to the reversed argument array.

Usage and lifecycle: a client builds and initializes a DISPPARAMS structure, fills rgvarg with VARIANTs (using VariantInit/VariantClear as needed), optionally fills rgdispidNamedArgs for named parameters, and sets cArgs and cNamedArgs before calling IDispatch::Invoke. The caller is typically responsible for cleaning up the VARIANTARG values after the call. If there are no arguments, pDispParams may be NULL with cArgs and cNamedArgs set to zero.