defaultvalue

interface interface-name
{

    return-type func-name(mandatory-param-list,
[[attribute-list,] defaultvalue(value)] param-type param-name[, optional-param-list]);

    }

Examples

interface IFoo : IUnknown
{
    HRESULT Ex1([defaultvalue(44)] LONG       i);
    HRESULT Ex2([defaultvalue(44)] SHORT      i);
    HRESULT Ex3([defaultvalue("Hello")] BSTR  i);
...
}
interface QueryDef : IUnknown
{
    HRESULT    OpenRecordset(  [in, defaultvalue(DBOPENTABLE)]
    LONG Type,
    [out,retval] Recordset **pprst);
}
 //  Type is now known to be a LONG type (good for browser in VBA and
//  good for a C/C++ programmer) and has a default value of
//  DBOPENTABLE
 

Remarks

The defaultvalue attribute allows specification of a default value for a typed optional parameter. The value can be any constant, or an expression that resolves to a constant, that can be represented by a VARIANT. Specifically, you cannot apply the defaultvalue attribute to a parameter that is a structure, an array, or a SAFEARRAY.type.

The MIDL compiler accepts the following parameter ordering (from left-to-right):

1. Required parameters (parameters that do not have the defaultvalue or optional attributes),
2. optional parameters with or without the defaultvalue attribute,
3. parameters with the optional attribute and without the defaultvalue attribute,
4. lcid parameter, if any,
5. retval parameter

See Also

interface, dispinterface, TYPEFLAGS, ODL File Syntax, ODL File Example, Generating a Type Library With MIDL