PropVariantToUInt32 function (propvarutil.h)

Extracts an ULONG value from a PROPVARIANT structure. If no value can be extracted, then a default value is assigned.

Syntax

PSSTDAPI PropVariantToUInt32(
  [in]  REFPROPVARIANT propvarIn,
  [out] ULONG          *pulRet
);

Parameters

[in] propvarIn

Type: REFPROPVARIANT

A reference to a source PROPVARIANT structure.

[out] pulRet

Type: ULONG*

When this function returns, contains the extracted property value if one exists; otherwise, 0.

Return value

Type: HRESULT

If this function succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.

Remarks

This helper function is used in places where the calling application expects a PROPVARIANT to hold a ULONG value. For instance, an application obtaining values from a property store can use this to safely extract the ULONG value for UInt32 properties.

If the source PROPVARIANT has type VT_UI4, this helper function extracts the ULONG value. Otherwise, it attempts to convert the value in the PROPVARIANT structure into a ULONG. If a conversion is not possible, PropVariantToUInt32 will return a failure code and set pulRet to 0. See PropVariantChangeType for a list of possible conversions. Of note, VT_EMPTY is successfully converted to 0.

Examples

The following example, to be included as part of a larger program, demonstrates how to use PropVariantToUInt32 to access a ULONG value in a PROPVARIANT.

// IPropertyStore *ppropstore;

// Assume variable ppropstore is initialized and valid

PROPVARIANT propvar = {0};

HRESULT hr = ppropstore->GetValue(PKEY_Rating, &propvar);

if (SUCCEEDED(hr))

{

     // PKEY_Rating is expected to produce a VT_UI4 or VT_EMPTY value.

     // PropVariantToUInt32 will convert VT_EMPTY to 0.

     ULONG uRating;

     hr = PropVariantToUInt32(propvar, &uRating);

     if (SUCCEEDED(hr))

     {

             // uRating is now valid

     }

     else

     {

             // uRating is always 0

     }

     PropVariantClear(&propvar);

}

Requirements

See also

InitPropVariantFromUInt32

PropVariantChangeType

PropVariantToUInt32Vector

VariantToUInt32