Although it seems at first that there is an error in the way this particular
parameter is declared, the declaration actually makes sense when you look at
the underlying mechanisms used by Macintosh Toolbox calls.
Because Macintosh Toolbox calls use Pascal parameter-passing conventions, an
AddrBlock parameter is always passed as the address to that parameter. This
happens because any parameter longer than 4 bytes automatically has its address
passed to preserve stack space.
To mimic this calling convention, the C declaration for the BuildDDPwds
declares the AddrBlock parameter as a pointer to an AddrBlock structure. When
you call the BuildDDPwds routine, you are expected to pass a pointer to an
AddrBlock structure you have declared.
For more information, see the Parameter types section of the "MPW C Reference."