Atoms and Shared Memory Objects
Certain arguments of DDE messages are global atoms or shared memory objects.
Applications using these arguments must follow explicit rules about when to
allocate and delete them. In all cases, the message sender must delete any atom or
shared memory object that the intended receiver will not receive because of an
error condition, such as failure of the
PostMessage function.
DDE uses shared memory objects for three purposes:
- To carry a data-item value to be exchanged. This is an item referenced by the hData parameter in the WM_DDE_DATA and WM_DDE_POKE messages.
- To carry options in a message. This is an item referenced by the hOptions parameter in a WM_DDE_ADVISE message.
- To carry a command execution string. This is an item referenced by the hCommands parameter in the WM_DDE_EXECUTE message and its corresponding WM_DDE_ACK message.
An application that receives a DDE shared memory object must treat it as read
only. The application must not use the object as a mutual read-write area for
the free exchange of data.
As it does with a DDE atom, an application should free a shared memory object
to manage memory effectively. The application should also lock and unlock
memory objects.
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