Type Indicators

The actual properties follow the table of Property Identifiers/Offset Pairs property set values. Each property is stored as a DWORD, followed by the data type value.

Type indicators and their associated values are described in the PROPVARIANT structure.

All Type/Value pairs must begin on a 32-bit boundary. Thus, values may be followed with null bytes to align the subsequent pair on a 32-bit boundary.

The following example code calculates how many bytes are required to align on a 32-bit boundary, given a count of bytes.


cbAdd = (((cbCurrent + 3) >> 2) << 2) - cbCurrent ;

Within a vector of values, each repetition of a simple scalar value smaller than 32 bits must align with its natural alignment rather than with a 32-bit alignment. In practice, this is only significant for types VT_UI1, VT_UI2, VT_I2, and VT_BOOL (which have one-byte or two-byte natural alignment). All other types have four-byte natural alignment. Some types, for example, VT_R8, actually have 8-byte natural alignment, but are stored as if they have four-byte alignment.

A property value with type indicator VT_I2 | VT_VECTOR would include:

  • A DWORD element count.
  • A sequence of packed two-byte integers with no null padding between them.

Important  Any 32-bit counts or property types that are stored as a part of a vector property element must also be 32-bit aligned.
 

A property value of type identifier VT_LPSTR | VT_VECTOR would include:

  • A DWORD element count (DWORD cElems).
  • A sequence of strings (char rgch[]), each preceded by a length-count DWORD and possibly followed by null padding to round to a 32-bit boundary.

 

 

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