IUnknown_Set function (shlwapi.h)

Changes the value of a Component Object Model (COM) interface pointer and releases the previous interface.

Syntax

void IUnknown_Set(
  [in, out]      IUnknown **ppunk,
  [in, optional] IUnknown *punk
);

Parameters

[in, out] ppunk

Type: IUnknown**

The address of a COM interface pointer to receive the pointer assigned to punk. If the previous value of the pointer is non-NULL, the function releases that interface by calling its IUnkown::Release method.

[in, optional] punk

Type: IUnknown*

The interface pointer to be copied to ppunk. If the value is non-NULL, the function increments the interface's reference count.

Return value

None

Remarks

This function mimics the behavior of a smart pointer. Conceptually, the function does the following:

• Releases the original interface, if ppunk is non-NULL
• Assigns punk to ppunk
• Calls IUnknown::AddRef on the interface pointed to by punk, if punk is non-NULL.

Examples

void sample()
{
  IUnknown *punk = NULL;
  IStream* pstm = NULL;

  if (SUCCEEDED(CreateStreamOnHGlobal(NULL, TRUE, &pstm)) {
    // since punk == NULL, this merely copies the value and AddRef()s it
    IUnknown_Set(&punk, pstm);
    pstm->Release();

    if (SUCCEEDED(CreateStreamOnHGlobal(NULL, TRUE, &pstm)) {
      // this call will release the old value of punk before copying the
      // new value and AddRef()ing it
      IUnknown_Set(&punk, pstm);
      pstm->Release();
    }
  }

  // This call will release whatever punk points to, if anything.
  IUnknown_AtomcRelease((void**)&punk);

  // at this point, punk == NULL
}

Requirements