PropVariantToStringVectorAlloc function (propvarutil.h)

Article
10/13/2021

Extracts data from a PROPVARIANT structure into a newly allocated strings in a newly allocated vector.

Syntax

PSSTDAPI PropVariantToStringVectorAlloc(
  [in]  REFPROPVARIANT propvar,
  [out] PWSTR          **pprgsz,
  [out] ULONG          *pcElem
);

Parameters

[in] propvar

Type: REFPROPVARIANT

Reference to a source PROPVARIANT structure.

[out] pprgsz

Type: PWSTR**

When this function returns, contains a pointer to a vector of strings extracted from source PROPVARIANT structure.

[out] pcElem

Type: ULONG*

When this function returns, contains the count of string elements extracted from source PROPVARIANT structure.

Return value

Type: HRESULT

This function can return one of these values.

Return code	Description
S_OK	Returns S_OK if successful, or an error value otherwise.
E_INVALIDARG	The PROPVARIANT was not of the appropriate type.

Remarks

This helper function is used in places where the calling application expects a PROPVARIANT to hold a vector of string values.

This helper function works for the followingPROPVARIANT types:

VT_VECTOR | VT_LPWSTR
VT_VECTOR | VT_BSTR
VT_ARRAY | VT_BSTR

If the source PROPVARIANT has a supported type, this function extracts a vector of string values into a newly allocated vector of newly allocated strings. The calling application is responsible for using CoTaskMemFree to release both the strings contained in the output vector, and the output vector itself, when they are no longer needed.

If a BSTR in the source PROPVARIANT is NULL, this function will place a newly allocated string containing "" into the output vector.

Examples

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

// IPropertyStore *ppropstore;
// Assume variable ppropstore is initialized and valid
PROPVARIANT propvar = {0};
HRESULT hr = ppropstore->GetValue(PKEY_Keywords, &propvar);
if (SUCCEEDED(hr))
{
         // PKEY_Keywords is expected to produce a VT_VECTOR | VT_LPWSTR, or VT_EMPTY
         // PropVariantToStringVectorAlloc will return an error for VT_EMPTY
         LPWSTR *prgKeywords;
         ULONG cElem;
         hr = PropVariantToStringVectorAlloc (propvar, &prgKeywords, &cElem);
         if (SUCCEEDED(hr))
         {
                 // prgKeywords contains cElem strings
                 for (ULONG i = 0; i < cElem; i++)
                 {
                          CoTaskMemFree(prgKeywords[i]);
                 }
                 CoTaskMemFree(prgKeywords);
         }
         else
         {
                 // propvar either is VT_EMPTY, or contains something other than a vector of  strings
         }
         PropVariantClear(&propvar);
}

Requirements

Requirement	Value
Minimum supported client	Windows XP with SP2, Windows Vista [desktop apps only]
Minimum supported server	Windows Server 2003 with SP1 [desktop apps only]
Target Platform	Windows
Header	propvarutil.h
Library	Propsys.lib
DLL	Propsys.dll (version 6.0 or later)
Redistributable	Windows Desktop Search (WDS) 3.0